rework 'notify in current chat' feature

* (focused) notification sound is customisable and separated from
default (unfocused) notification sound
* now also works w/o persistent notification
* obeys system sound state (will vibrate if sound is off and vibration
is enabled) - useful for 'quiet hours'
* will not show a visual notification banner anymore (only
sound/vibrate)

known quirks:
* will sometimes play if user ticks/unticks 'taskbar icon' in settings
(needs to be revisited)
add an option to hide message count in notifications
notification: adjust avatarsize and left padding
for sdk>=14 to match common aosp defaults
notification: show contacts name in ticker