Implement generic support for password in atvremote

[postlund]

What feature would you like?

With 0.9.0, password is now a general setting for all protocols. It is only relevant for RAOP at the moment (and AirPlay in the future, once support is added for that). I however would like to add generic support in atvremote for the sake of being generic.

Describe the solution you'd like

Should accept arguments on the form --xxx-password where xxx is one of the protocols (e.g. airplay or raop). Password should be set for the correct service.

Any other information to share?

This is an easy task, suitable for someone new.