This allows simpler server-side code, and a failure part-way through sending won't require restarting from the beginning next time.

Also, don't support unverifying contacts.

Closes #580

Also includes unit tests for the new message types.

Closes #591

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

Closes #579

Fixes #470

Closes #486

This is done by remembering the time of the latest entry.
All entries newer than that are considered new and will be posted.

Closes #485

* Implemented in briar-core as a `ScheduledExecutorService`
  that gets started when the app starts
* The briar-api has a `FeedManager` interface
  that the UI can use to register and unregister feeds
* In this first iteration, feeds are fetched via HTTP(S), not Tor

Closes #484

Closes #472

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

This prevents trying to access the same group metadata in different groups.
Also, the conversation does not need to be reloaded once introduction messages arrive.

Closes #535

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

This is useful when sorting blog posts in the combined feed. It ensures
you do not miss older posts that were just synced to you.

When a contact is added, her personal blog will also be added automatically.
Also, when a new identity is added, a personal blog for that identity is created.

Part of #436

Removes teaser and makes body mandatory.

It also adds support for deleting blogs and
introduces a getAuthorStatus() method to the IdentityManager
that takes a running transaction.

Closes #441

This implements a simple initial blog client that covers the basic blog
actions, but no deletion/removal of blogs, yet.

Classes for Blogs and Blog Post Headers have been introduced along with
the associated factories.

A `BlogPostValidator` has been added that validates incoming blog posts.

Closes #402
Closes #404

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.

This change will allow to pass message dependencies from the client
validators to the ValidationManager.

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

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

Added support for retrieving metadata that matches all key/value pairs in a query.