Refactor the way objectionable items are stored (Bug #1298646)

- Created 'objectionable' table
- Migrated existing objectionable records to a new table
- Added is_objectionable() method to View class
- Fixed can_view_view() and elasticsearch to use new table
- Fixed artefact.tpl style to match view page when displaying "Not objectionable" form
- Make forum reports use new 'objectionable' table

Change-Id: Ib3759e86c4003216ad57f3cf68911b13e50e9c67
Signed-off-by: Yuliya Bozhko <yuliya.bozhko@totaralms.com>