Fixes and improvements in mentat-reporter.py module.

There was a bug in reporter module, that caused the events_thresholded cache to be entirely stripped off of any records after each reporting cycle. The cleanup algorithm was all wrong, so the relapse mechanism could never work. This issue is fixed now, but it was necessary to alter SQL schema and make some additional API changes to make everything work. Additionally to have more control over the reporting process the logging features of the module were improved. (Redmine issue: #3378)