Use associaton table to link groups and reports. (Redmine issue: #7052)

conf/templates/reporter/default.extra_v2.txt.j2

conf/templates/reporter/default.summary_v2.txt.j2

lib/hawat/blueprints/reports/__init__.py

lib/hawat/blueprints/reports/templates/reports/search.html

lib/hawat/blueprints/reports/templates/reports/show.html

...ersions/b450d1c91e82_map_group_report_relationship_by_.py

lib/mentat/datatype/sqldb.py

lib/mentat/datatype/test_sqldb.py

lib/mentat/reports/event.py

lib/mentat/reports/test_event.py