SW-402: merged ltastorageoverview from trunk into LOFAR-Release-3_1 for deployment to production as per request by SOS/SDOS

SW-402: copied srm_url addition to event dict from ltastorageoverview branch into release branch, so yan can use it for an sdc demo

SW-283: processed review: factored out insert_missing_directory_tree_if_needed from one method in ingesteventhandler to multiple reusable methods in LTAStorageDb

SW-283: start IngestEventHandler with configurable and proper default options in scraper, so that the scraper will automatically visit the recent additions from ingest.

SW-283: added method to get a dir's last visit time. added argument in directoryByName to filter for given site_id

SW-283: pass along the srm_url from the dataproduct notification to the task notification if possible

Task #8721: SW-280: processed review comment: added some tests for the scraper Location class. made some minor changes to the scraper module. Not going to do a full refactoring; I agree some methods in scraper.py are too big, but they are self contained and not part of a public API. So it's good enough for now.