Integrate Totara Report Builder into core

Totara has a custom report builder that allows users to create custom reports via the GUI and save them.

Docs: http://help.totaralms.com/site_admin/SA_Report_Builder.htm
Example: http://help.totaralms.com/Totara_captivates_help_1_1/reporting_scenario_v1/reporting_scenario_v1.htm

Let's look at getting it into Moodle core:

Most of the code is in /local/reportbuilder with activity modules providing some "report sources" in mod/xxxx/rb_sources/xxxx.php

At a first guess, I think it could move to /report/reportbuilder with module-specific classes in mod/xxxx/reportbuilder.php