Add ability to skip auth in specific modes

The configurator knows the general active mode and exposes a function to check for it.
It's also the only place to instantiate Auth instances.

Auth instances can now be configured with an array of `skipModes` - modes where the authentication routine is circumvented.

The configurator passes the mode function to the Auth instance, so that it can check if authentication is required or not.

Check how the perseids authentication configuration does it.

Closes #458