[REFACTOR] moved FileList classes

They are mainly used in the classes of the invitation packet and so this
should be the right place.

Change-Id: Iaec7d524a248837a7e4201301254721d0730b139
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1205
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>