Updated `UserGroups` and `Users` models:
- `UserGroups` now use tree behavior, to enable group nesting.
- Added helper method to `Users` to enable retrieve group with user data to `Auth`.
Updated bootstrap `access` config. Added `query` method to active usess `Auth` configuration.
Added initial `CHANGELOG.md`.
Updated migration files to use `models` instead of `source` to disable direct access to DB tables. Added basic access rules.