[GUI|UX] detailed sound playback selection

This patch allows the end user to select which sound
events/notifications should be played or not. Currently all four sound
events are supported: contact comes online/offline and chat message
sent/received.

Change-Id: I9ac0f6d3e405e0b6b1c1b152a728ff94dcb34aaf
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1183
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>