Add new "uses" parameter to ActionFactory methods, allowing additional fixtures to be provided for specific controllers

[laundmo]

This PR adds a new arguments to ActionFactory.__call__ and the individual HTTP method calls.

It also improves documentation for ActionFactory/convenience decorators.

Motivation:
The convenience decorators, while nice, were previously quite limiting. Users had to either create a new convenience decorator for every combination of fixtures or avoid using them entirely. For example, checking groups permissions with a fixture like the docs recommend was a hassle to do, as it would require an ActionFactory instance per group.

This allows the following to work:

@authenticated(uses=[requires_group("admin")])
def admin_dashboard():
    return dict()

or alternatively using HTTP method specific calls

@authenticated.get(uses=[requires_group("admin")])
def admin_dashboard():
    return dict()