Also react to incoming group invitations

Also removes support for anonymous forum posts.
Closes #698

Also fixed a couple of bugs.

This way the forum and private group client do not need to keep track of
message timestamps themselves and do not need to interact with
post/message factories.

Also made some listeners volatile.

and maintain keyboard state when hiding view.

Fixes #531, #532

Fixes #373

This commit also moves various blog classes into their own packages and
makes the required visibility changes.

in group metadata to be able to speed up group listings.

Closes #584, #586, #585

All text that can be generated by users will show emoji from the
shipped sprites.

For all messages and posts, the custom emoji keyboard is now available.

This also disables menu actions rather than hiding them and thus
closes #677

Included is a fix for a regression that was not showing the keyboard
automatically in forums and thus
closes #676

Add functionality to save and restore recently used Emojis

Update emoji and add new categories based on AOSP's XML file

Comments and reblogs need to depend on the post they refer to.
Since message dependencies are limited to one group,
the post and also the comments need to be wrapped
when commented on or reblogged to another blog.

For this reason, in addition to comments, two new wrapping message types
are introduced. They retain all data of the original messages and allow
for reconstruction and signature verification.

This commit breaks backwards compatibility with old blog posts.
It removes the content type, title and parent ID from the post
message structure.

Fixes #539, #564 and #568.