added a cache to the IdentityManager, changed its signature, modified when and where the author is stored

made the author creation single-threaded again in the LifecycleManager, removed redundant code

Implement UX for viewing the membership of a private group

This MR is the second and last MR to address #678. The first part is in !377.

![device-2016-10-26-112000](/uploads/8cbdee65c123a6d5329e208d9983d0b0/device-2016-10-26-112000.png)

Closes #678

See merge request !364

Remove content-type and parentId from private messages

and turn them into a regular string.

Closes #600

See merge request !372

Implement UX for when a group has been dissolved

This MR is based on !367.

Closes #672

See merge request !369

Implement UX for leaving a group

This MR also includes the creator's part of the UX for dissolving a group since it is almost the same.

![device-2016-10-26-185615](/uploads/8689a1ee103fcee23105a469b37c59de/device-2016-10-26-185615.png)

Closes #671

See merge request !367

Update blog backend to match current usage

Closes #700

See merge request !371

and turn them into a regular string.

Remove forum content type and change bodies to string

Also removes support for anonymous forum posts.

This MR depends on !360.

Closes #698, #681

See merge request !370

Add methods and hooks to PrivateGroupManager related to members and removal

This MR is the first of two MRs related to #678.

See merge request !377

Refactor contact lists, their adapters and items

This was supposed to be a preparation for #678 to make the contacts lists cleaner and easier to re-use for different use-cases. Turns out #678 can't use this work, but it is probably nice to have anyway.

During this work, support for multiple identities has been removed from the various contact lists.

See merge request !363

Implement protocol for private group messaging

Closes #708

See merge request !360

Also removes support for anonymous forum posts.
Closes #698

Implement UX for showing and answering private group invitations

As usual, this MR contains several logically separate commits that could be split out into smaller MRs if desired. It consists of two main parts:
* Showing open invitations in the list of private groups with a snackbar
* Showing invitations and responses in the private conversation

For both parts, the existing code was refactored to allow for a smooth implementation and to leave maintainable code behind.

![device-2016-10-18-101549](/uploads/66582dbe97736fdcd2498e87e1c7dfd1/device-2016-10-18-101549.png)
![device-2016-10-18-101612](/uploads/8c25eff8171f330796a55cb27cdb2552/device-2016-10-18-101612.png)
![device-2016-10-18-101534](/uploads/ebba4c0a2c0f727dcadac8c2ec57b48f/device-2016-10-18-101534.png)

Closes #707

See merge request !357

ProtocolStateException for client protocols

Methods that implement local actions in a client protocol (for example, accepting an invitation) can throw this exception to indicate that the action wasn't taken because the action isn't applicable to the current state. This can happen if the protocol state machine is updated by an incoming message and the user takes an action before the UI has been updated.

See merge request !368