Also properly handle back navigation when trying to add contacts.

Closes #342

Only personal blogs from non-contacts can be removed.
This also adds integration tests that check if blogs can actually be removed.

Closes #579

This refactors the forum invitation code,
so it can be used by both: forums and blogs.

This commit refactors the code for sharing forums,
so it can be used for sharing blogs as well.

It does not yet include code for responding to blog invitations.

Closes #517

This also adds a setting allowing people to turn blog post notifications off.

Closes #488

Closes #472

Closes #415

Closes #533

* 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

Closes #360

Closes #455

This commit addes a combined blog feed that shows all posts of all
subscribed blogs in the order the blog posts have been received.

For now, this commit also hides other blog functionality like adding
additional blogs and browsing individual blogs.

Closes #417

Closes #418

This allows for swiping left/right to read other posts by using
a ViewPager.

This hasn't been done as a separate activity, but with
fragments, so both can share the `BlogPersistentData` without
needing to reload it.

Closes #428

Closes #411

This commit lays the groundwork for #415

This does not yet support multiple identities. It just shows blogs
created by the first identity, but can easily be adapted for
multi-identity support.

Closes #410

Clicking the plus in the toolbar open the `CreateBlogActivity` which
allows the user to create a new blog. Only the first identity is
considered, but support for more identities can be easily added later.

The actual list of blogs in the My Blogs tab will be done in the next
commit.

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

Closes #327

Once applied this commit will change the font colors according to the
design and move all themes into a dedicated file.

Closes #333

This replaces the custom layouts in the navigation drawer with a
`NavigationView` and adds a menu entry for Blogs.

A Main Blogs fragment is added that holds a `TabLayout` and a
`ViewPager`. Five tabs are already added, but they just have a single
placeholder fragment that is to be replaced by the actual fragments.

Closes #409

It does so by extending the compound view `TextAvatarView` and provides
convienient setters that take care of the required UI changes.
The new badge can also be used to indicate a problem with the forum.

Closes #408

The new activity shows who you are sharing a forum with and who shares a
forum with you. It is accessible from the overflow menu when in a forum.

Closes #398

Closes #399