[INTERNAL] Split all IActivityProvider into Producer/Consumer

This patch introduces a AbstractActivityConsumer which offers standard
implementations for both IActivityConsumer's dispatching exec() method
*and* IActivityReceiver's making-activities-type-safe receive() methods. 
A lot of classes could be simplified by using this new default
implementation.

This patch deletes all obsolete interfaces and classes. The JTourBus
tours and other documentation have been amended where necessary and
appropriate.

Change-Id: I97d07cf4a87bcd4e1224620544396c7895be98cb
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1617
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>
Tested-by: Jenkins-Core QA
Tested-by: Jenkins-Eclipse QA
Tested-by: Jenkins-IDEA QA
Tested-by: Jenkins CI
Reviewed-by: Franz Zieris <zieris@inf.fu-berlin.de>