[API] Adds SarosSessionManager and SarosSession

Change-Id: I35d9cf6f5c0d9b72bff9edb33439641f11cf294a
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1890
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>
Reviewed-by: Holger Schmeisky <google@schmeisky.com>