Improve terminal select / multiselect

[christerswahn]

In the prompts library, the select() and multiselect() functions need some improvements.

• Do not throw ExitException if the user quits, instead return null and let the caller be responsible for how to act.
• If possible, allow the user to press ESC to quit the selection (in addition to the current 'q').
• Inform the user they can press q / ESC to quit.
• Do not clear the screen upon render / rerender, instead just rerender the lines of the select prompt.