[INTERNAL] Add DecompressTask (invitation-related)

Change-Id: Ia056dfe5f5a1cf1127151c918cf7c547242c162b
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1659
Tested-by: Jenkins CI
Reviewed-by: Franz Zieris <zieris@inf.fu-berlin.de>