This fixes a bug that prevented client shutdown if the client failed to
completely initialize during address book loading.

This ensures files that are unlikely to be KX files are not loaded
during startup.

This is added to the /addressbook command, as an optional argument to
display the addressbook entry of a particular user.

This resets all clients with ratchets that have not received messages in
a given age.

This allows showing the last time a message was received from all users.

This adds a check after connecting to the server to verify if the local
client has been offline for longer than the server's message retention
policy. If true, then the client sends a reset KX command to all known
users.

This is needed to prevent a situation where, after being offline for too
long, all of the client's ratchets are broken due to lost messages.

Instead of using a fixed 7-day interval, use the server expiration
policy.

Improves performance when there are many KXs.

Needed to debug test failures

Also add a confirmation modal to the block user action.