[REFACTOR] moved various model classes to simplify package layout

Change-Id: I7b891c5ddbfdae9eb266573fdad7bd914bf4482d
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1554
Reviewed-by: Franz Zieris <zieris@inf.fu-berlin.de>
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>