[#2409] Tested all auth setup configs in AuthTestControllerTest. Adjusted :skip_plug definitions for some endpoints.

Fixed OAuth restrictions for :api routes. Made auth info dropped for :api routes if OAuth check was neither performed nor explicitly skipped.

Automatic checks of authentication / instance publicity. Definition of missing OAuth scopes in AdminAPIController. Refactoring.

Add specs for AccountController.mutes, AccountController.blocks, AccountController.mutes, AccountController.endorsements

Enforcement of OAuth scopes check for authenticated API endpoints, :skip_plug plug to mark a plug explicitly skipped (disabled).

Ability to control the output of account/pleroma/relationship in statuses in order to improve the rendering performance.
See `[:extensions, output_relationships_in_statuses_by_default]` setting and `with_relationships` param.

Admin API: `PATCH /api/pleroma/admin/users/:nickname/credentials`, `GET /api/pleroma/admin/users/:nickname/credentials`.

Unless the timeline belongs to a blocked user.

[#1335] Implemented notification mutes and reblog mutes as UserRelationships. User to UserRelationship relations and functions refactoring.

Introduced UserBlock.

Misc. fixes / improvements.