Task #8691: INSTALL: add python-django dep for SAS/Trigger_Services. On Ubuntu and CentOS this pkg is named the same.

Fix merge conflict on momqueryservice.py. Moved on trunk, but changed on this branch.
Solve by replacing the moved file with the changed file (thus, move the changed file over the moved file).
Careful checking of (JD's) changes shows this is correct; the changes are preserved.
Other moved files did not cause conflicts, since they were not changed.

Task #8691: update INSTALL for some optional SAS pkgs, and for Ubuntu 16.04 libgsl pkg name as AOFlagger dep

Task #8161: tDelayAndBandPassKernel2: remove confusing and unused parset keys referring to test data in custom location

Task #7874: replace README, add INSTALL, COPYING (GPLv3), remove out-of-place, out-dated releases.txt. INSTALL can be extended later.