[FEATURE] Ask server for session information

Ask the server whether he is in a running session and (if yes) how many
participants and which projects are included.

Feature is not yet activated.

Change-Id: I949db8764e0c35a147c278cd632b1fc9bcbf0ae7
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1293
Reviewed-by: Arndt Lasarzik <alasarzik@gmail.com>
Tested-by: Jenkins CI
Reviewed-by: Franz Zieris <zieris@inf.fu-berlin.de>
Reviewed-by: Nils Bussas <nils.bussas@gmail.com>