[REFACTOR] moved chat interfaces and SUC implementation to Saros Core

Modified the ChatElement class as it contained rendering stuff for a
GUI. Moved this logic to the ChatControl class.

Change-Id: Ie72e3d5020ed3b1520708c2db21148bf0e810bab
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1438
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>