SW-699: added UsingToBusMixin, and (re)use that in all the ServiceMessageHandlers and some AbstractMessageHandler derivatives

SW-699: Use exchange,routing_key syntax for AbstractBusListener constructor, drop use of **kwargs, fix IngestEventHandler as it was still propagating subjects to listen for

SW-699: Make notifications unconfigurable, greatly reducing complexity of the higher abstraction layers.

SW-699: Use a single broker and bus (exchange), and make service names unconfigurable (fixed in Service and RPC). Greatly reduces configuration size.

SW-0: moved the cep4_utils.py file from QA to LCS/PyCommon, and fixed references. Needs to be adapated in https://svn.astron.nl/LOFAR/branches/adder-Task10079 as well.

SW-0: another manual merge (manual file copy) from https://svn.astron.nl/LOFAR/branches/adder-Task10079

Task #10079: another manual merge (manual file copy) from https://svn.astron.nl/LOFAR/branches/adder-Task10079

SW-401: merged new QA_Service developments from trunk, which came via a manual merge (manual file copy) from https://svn.astron.nl/LOFAR/branches/adder-Task10079

SW-401: another manual merge (manual file copy) from https://svn.astron.nl/LOFAR/branches/adder-Task10079

Task #10079: manually copied parts of the QA package into LOFAR-Release-3_1. This allows us to roll out a new LOFAR-Release-3_1 on the scu with an extra QA_Service. The QA_Service hardly depends on anything, and doesn't require modifications to the rest of the lofar code. This makes this unusual manual merge acceptable. The rest of the QA code is not part of this release, and is not merged to this branch (yet). It runs isolated in docker containers on cep4.