The toolbar subtitle shows information about how many contacts the
current blog is shared with and how many of those are online.

* Remove distinction between "shared with" and "shared by"
* Show all contacts a blog is shared with
* Show online status of contacts in sharing screen

This adds a sign() and a verify() method to the CryptoComponent
that take a mandatory label argument to ensure that signatures can't be
repurposed.

and make sure work is offloaded to an executor, so exceptions can be
caught.

because they are not shown in the UI and are therefore not marked as
read. This fixes the unread message count.

This also adds two integration tests and improves some small details