Automatically link screens

[mikldt]

The workflow for creating a new player is to click the Hardware: add link in screens/show. Right now, the user has to then enter the screen ID in the player#new form once they click the link.

Instead, we should pass a screen_id GET parameter as part of that link, and use that for the new player. It would probably make sense to hide the Screen ID field (since there's no reason to change it) and just show the screen name.