[11.x] Use Gate Facade due to updated BaseController

[Jubeki]

Mainly to make you aware of changes to be made due the skeleton slimming, where traits are removed from the Base Controller: See https://github.com/laravel/laravel/pull/6188/files#diff-6eba513804f3952156d999eea3fb21199659f395d0092da71a10868b72bf59ce

• $this->authorize(...) will not be available, but can be replaced with Gate::authorize(...)
• $this->authorizeResource(...) will not be available without the trait, the method is currently not implemented in Illuminate\Auth\Access\Gate therefor marked as TODO