Remove PersistentData classes as they aren't thread-safe

This MR depends on !244 and does not claim to resolve *all* issues with the ForumActivity.

Closes #544

See merge request !253

Introduce client layer events for forums

The forum UI depended on sync layer events such as `MessageStateChangedEvent`.
Now, the forum client broadcasts its own high-level event (`ForumPostReceivedEvent`)
with the information the UI needs (`ForumPostHeader`).

Closes #310

See merge request !244

Database queries for metadata only returned it for messages that were delivered already.
However, there are cases (e.g. a pending message needs to be delivered) where
the validator needs to retrieve the metadata from the database.

For these cases, a special database query has been introduced.

The forum UI depended on sync layer events such as MessageStateChangedEvent.
Now, the forum client broadcasts its own high-level event (`ForumPostReceivedEvent`)
with the information the UI needs (`ForumPostHeader`).

Closes #310

Explain why forum can't be shared with contact

Closes #533

See merge request !252

Closes #533

Merge branch '515-starting-intent-from-preferences-does-not-work-with-different-app-id' into 'master'

Allow different package IDs (for preference intents)

Closes #515

See merge request !248

Closes #515

Micro Blogs UI

**Attention:** This MR includes several other commits which are supposed to end up in separate MRs. I suggest that you review **per commit**. Once the first two commits have green light, I can split out the other commits into other MRs. This way I don't have to work myself through a long rebase chain every time I make a change to the bottom MR.

This MR is full of commits that introduce features that we will not be using initially. The last commit implements the Micro Blogs UI on top of the framework the first commits establish and hides/disables all future features for now.

I suggest we merge this as is and clean things up later when we have a clearer idea what features we will be doing eventually.

![device-2016-06-23-135016](/uploads/600fc7c28c0c6c4a60d8273ffb55f30a/device-2016-06-23-135016.png)
![device-2016-06-22-181934](/uploads/e57cfbc162150bcd01d4683d4164406e/device-2016-06-22-181934.png)
![device-2016-06-23-142422](/uploads/5814f1e13b6d2230f2e4c12a8c5cd599/device-2016-06-23-142422.png)
![device-2016-06-23-142506](/uploads/d3ac268082b98bbcd068f3d6fe0c6712/device-2016-06-23-142506.png)
![device-2016-06-22-181913](/uploads/f5dcc1ed9a40ec5fa8f634864903f4cc/device-2016-06-22-181913.png)

Closes #436 

See merge request !214

Make it clearer who will be introduced

Show contact names under avatars before sending introduction to make it clearer who will be introduced.

![device-2016-07-08-121836](/uploads/de13f6e75b9a573e561e9c810bbdb08b/device-2016-07-08-121836.png)

Closes #356

See merge request !242

Show all Forum Invitations, not only the first one to prevent cut-offs and forks

This MR solves the problems outlined in #461 by always showing forum invitations, even if the user already subscribed to the forum.

Available Forums have been renamed to Forum Invitations in the UI:

![device-2016-07-07-144141](/uploads/9c8d06decdd19117250e3faca0c38192/device-2016-07-07-144141.png)
![device-2016-07-07-144150](/uploads/9803f567c962a721b24d79359974a29f/device-2016-07-07-144150.png)

Closes #461

See merge request !241

Improved the contact addition header

Closes #459

See merge request !245

Set focus mode properly when scanning QR codes

This simple fix contributed by @m8r-v9bo74 fixed the issue on my Xperia
Pro that could never focus on the QR code before. Focusing and scanning
still works on my other test devices.

Closes #346

See merge request !243

Show Snackbar after introduction request has been sent

Closes #360

See merge request !239

Improve Account Setup Screen

* Explain what "account creation" means on first run (#151)
* Use hints instead of dedicated text views
* Move password strength meter up into the user's view
* Always move user's view to current input field
* Improve "Forgot Password" dialog

![Screenshot_20160627-142116](/uploads/7fadc812f62c5f22f6ba73735d139064/Screenshot_20160627-142116.png)
![Screenshot_20160627-142127](/uploads/da27fb864bbe34168665a51b60747181/Screenshot_20160627-142127.png)
![Screenshot_20160627-142135](/uploads/19ddb247a043f56f9429a98e9655cd9f/Screenshot_20160627-142135.png)
![Screenshot_20160627-142153](/uploads/5d859e029a9584598a5cd6a391e697d3/Screenshot_20160627-142153.png)
![Screenshot_20160627-142204](/uploads/f59a79fc30528a17aece31f2c45d4638/Screenshot_20160627-142204.png)
![Screenshot_20160627-142241](/uploads/a493df940ae69b7ae1eecba598b4d378/Screenshot_20160627-142241.png)

Please note that the dialog button colors will be changed in !214 to the official design. Here they have the old colors.

Closes #151, #207

See merge request !229

This simple fix contributed by @m8r-v9bo74 fixed the issue on my Xperia
Pro that could never focus on the QR code before. Focusing and scanning
still works on my other test devices.

Closes #346

* Explain what "account creation" means on first run
* Use hints instead of dedicated text views
* Move password strength meter up into the user's view
* Always move user's view to current input field
* Improve "Forgot Password" dialog

Closes #151

to make it clearer who will be introduced.

Simple Empty State Messages

This MR implements very basic and simple empty state messages for the
current features.

This is how it looks (note that the contact add FAB will be removed soon):

![Screenshot_20160629-125146](/uploads/4c6a8be041cc48b0aba165dd507453d5/Screenshot_20160629-125146.png)
![device-2016-06-29-130834](/uploads/821677074d7d3e6435574a0711f3a0a7/device-2016-06-29-130834.png)
![Screenshot_20160629-125138](/uploads/a39a465db51f8e009ab0b6ee34d4a7e7/Screenshot_20160629-125138.png)
![Screenshot_20160629-125853](/uploads/1dab114bbe7ba379b20a5d298c8fa25c/Screenshot_20160629-125853.png)

Closes #327

See merge request !236

even after re-sharing an existing forum.

Removed the Fab and moved the icon into the toolbar

Closes #449

See merge request !240

Hide Identity Selector When Adding Contact

Closes #452

See merge request !233

Update Timestamps Every Minute

Yes by using `notifyDataSetChanged()` I am invalidating everything, but view binding is very fast and the RecyclerView is smart about it. I could parse the dataset and use `notifyItemChanged()` only on the elements that matter, but this is not generic and a lot more code which is not necessarily faster. I suggest we go with my simple and generic approach for now and optimize when we actually notice a performance problem.

Closes #455

See merge request !238

Closes #360

Closes #452