[INTERNAL] switched JID map to User map

The AwarenessInfo.Collector used JID to keep track of users. Most
business logic should not be aware on how a user is addresses but simply
use the user objects to perform business logic.

Change-Id: Ic88cb7c378695ed1841f7b2d8affe31662fd695a
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1623
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>