This adds a new table to the database to hold message dependencies.
It introduces two more message states: pending and delivered
The valid column in the database was renamed to state to better reflect
its new extended meaning.

The DatabaseComponent was extended with three methods for:
* adding dependencies
* getting dependencies of a message
* getting messages that depend on a message (dependents)
* getting messages to be delivered (by startup hook)
* getting pending messages to be possibly delivered (by startup hook)

In order to reflect the new states, things that were previously true for
VALID messages have been changed to now be true for DELIVERED messages.

Since pending messages should not be available to clients, many database
queries have been modified to only return results for delivered
messages.

All added methods and changes should come with updated unit tests.

Please note that the database version was bumped in this commit.

Fixes the following crash that occurs after upgrading to support 23.3.0:
https://code.google.com/p/android/issues/detail?id=174871

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 #391

Closes #399

Closes #396

The code for creating forums in ForumManager was used by
ForumSharingManager and also needed by InviteeEngine.
This extracts it into its own class.

Closes #375

Closes #395

Closes #374

Also prevents the snackbar from hiding the bottom of the list.

Closes #337

Switched AppBus for ResultHandler, Controller for Helper. Added the basics for LifecycleControllers and implemented it for BriarActivity and NavDrawerActivity