text options for screen_prompt

`screen_prompt` currently does not allow control of text size, color, etc. (as `screen_text` does). This change addresses that.

There is some repeated code, but I wasn't sure how best to get around that. Let me know what you guys think.
Oh wait, does it match the order of `Text`? It looks like the arguments are not in the same order as the docstring here, at least.