For a start, use android-logger as backend. Needs a better configuration
but no time right now.
For file-logging we will use logback as slf4j-implementation.
Conversations accepted our PR, so we will continue to get these intents.
The option cann still turned off, in that case Conversations' notifications are
picked up by our generic notification support.
If these get turned on, Conversations notifications will be handled through Pebble message intents and get filtered out from generic notifcation handling.
This enables support for Conversations without using generic notificaion support.
Other applications could also work partly but are untested.
This commit also changes the SettingsActivity to use Comboboxes instead of two
Checkboxes for each notification source.
