[INTERNAL] removed XMPP status information from user element class

Also cleaned up this class, making all fields private, the class final
and cleaned if nested if/else blocks. Changed the return value of the
getUser method from Object to User.

Change-Id: I187925ff2e8cc00cb766a5c6fc05802f7333357f
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1721
Tested-by: Jenkins-Eclipse QA
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>