Add functionality for specifying allowed submodules and frontend submodules

[adam-buckley]

Currently no support for having allowed submodules, i.e. not letting the whole module pass authentication, but only a submodule.

Also cannot point frontend configurations at a submodule, that would allow for configurations such as:

• example.com => /modules/example
• api.example.com => /modules/example/actions/api/

That would avoid devs having to make another module just for a frontend configuration and avoid having to specify the submodule in the path, e.g. api.example.com/api/