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.
Also, usually we might be concerned that the argument `wrap` has changed position, but in this case it's so far down the arguments list that I doubt that people have used positional arguments to specify it. And if they did, it will be clear that there's a problem.