Closes #593

Closes #616

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.

Also replace more raster graphics with vector graphics.

Closes #311

Fixes #539, #564 and #568.

Also properly handle back navigation when trying to add contacts.

Closes #342

Closes #587

No more general disabling of abortOnError
Resolved all *errors* beside language ones  MissingTranslation & ImpliedQuantity
Issue context: #567

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

Briar crashed when run in a device without bluetooth or without camera
such as an emulator.

Closes #514

Fixes #572, #578.

Closes #565

Closes #429

When we clear a list in onPause(), the proper behavior is that the empty state
message is shown, because the list is indeed empty.

However, we will reload the list content again in onResume(),
so the fix chosen in this commit is to force showing the progress bar
right after clearing the list.

Closes #576

This refactors the current SharingStatusActivity
so it can be used for forums and blogs.