17 lua console

Adds a long-overdue console window to Thrive (issue #17). It's available everywhere, toggled by pressing ` (the backtick key), has persistent command history (persistence across runs requires some tweaking) that you can scroll through with up/down, and evaluates everything as lua snippets in the same namespace as all the scripts. It currently does not eat key events, which is mildly inconvenient. print() is redirected to the console window, which might be a bad idea, but it is easily disabled.

Try it out, lemme know if anything should be added.