[API] Create IProgressMonitor in Saros/Core

This interface comes along with a simple implementation (in Saros/Core)
and an adapter/adapter factory (in Saros/Eclipse).

Change-Id: If8530e7e6f5def789cb253663c6b22416bfea5d9
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1507
Tested-by: Jenkins CI
Reviewed-by: Martin Wichner <martin.wichner@googlemail.com>
Reviewed-by: Arndt Lasarzik <alasarzik@gmail.com>
Reviewed-by: Franz Zieris <zieris@inf.fu-berlin.de>