Updated to higher API level

Removes backwards compatibility which now breaks the build on recent SDK
releases.
Add logging to OTRManager
Update to a more recent otr4j implementations

This takes the implementation from languitar/otr4j with all feature
branches enabled and modifies the xabber source code to comply to the
new API.
Hack: notifications in case of unreadable otr messages

Hacky implementation of showing at least something in case an unreadable
otr message is received.