Lofar release 4 0

Resolve SW-826

See merge request !69

SW-826: adding Casacore.casa as dependency on LCS/Common makes many lofar libs dependend on 3rd party libs which we don't actually use. This hinders us in deployment and maintenance on various systems. Hence, I removed the hard dependency on Casacore.casa, and made the empty-stub-CasaLogSink print out a warning message to cerr.

SW-826: adding Casacore.casa as dependency on LCS/Common makes many lofar libs dependend on 3rd party libs which we don't actually use. This hinders us in deployment and maintenance on various systems. Hence, I removed the hard dependency on Casacore.casa, and made the empty-stub-CasaLogSink print out a warning message.

SW-826: only insert predecessor/successor links into the radb when needed, thus preventing unneeded error log lines about duplicate keys

SW-826: fixed the taskprescheduler by letting it respond to RA.TaskApproved events and by NOT inserting/updating the task into the RADB.

SW-826: the taskprescheduler should NOT insert the task into the RADB. Added that requirement to the test, which now fails. Next commit has the fix for this bug.