== Initial approach ==
* New command to add/remove flag groups to/from users globally (2)
* New command to create and delete flag groups, and change flag to flag group assignments (3)
* Database storage for flaggroups - `flaggroup` (db table: 1, repository, model, mapping: 1 = 2)
* Database storage for flaggroup to global user assignments - `flaggroup_user` (db table: 1, repository: 1, model, mapping: 1 = 3)
* Existing class tidy-up (1)
* New `IFlagService` implementation (3)
* Bin old `LegacyFlagService`, `Access` command (1)
* Rip out any unused code (likely the entire legacy command system (0-5)