[REFACTOR] Move almost all packet extensions to core

All but two packet extensions are now in the core (package
communication.extensions).
The remaining classes in Saros/Eclipse are ProjectNegotiation-related
and they depend on "FileList" which is not yet decoupled from Eclipse.

Change-Id: I593c172543b1f0f7db6b55be4be38809885f52e0
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1491
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>
Reviewed-by: Andrej Szaffranietz <a.szaffranietz@gmail.com>
Reviewed-by: Franz Zieris <zieris@inf.fu-berlin.de>