[INTERNAL] moved feature query to content provider

It was very odd on how the RosterEntryElement was responsible for
updating its Saros Feature status. The query is now done in the content
provider instead.

Change-Id: I4502707caa277223af96397c070e92bf3c21a344
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1948
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>