Scroll Bars (Well, vertical, anyway.)

horizontal will be a fairly trivial generalization.
generalized to h scrollbars

one thing left for scroll bars - timers to auto-repeat scroll on buttons
while held - and they're complete!
added suicide to drag repeat timer on text fields

also, won't be doing that auto-repeat I mentioned for scroll bars after
all. no mouse_up, just drop after drag, because I quite specifically
said that was all that was needed. Dumbass.