(BlackBerry) Fix overlay issues including multitouch weirdness.

Tried to keep it simple originally but it missed a number of cases where the order of touches and releases caused ignored buttons. The function qnx_input_state stops polling the overlay when it returns a 0. There could be more valid touches after that with the old method. Now I keep track of all the valid touches in touch_map to ensure we don't miss any while keeping logic out of the state polling.

Fixed a regression on BB10 where the screen_width and screen_height weren't set properly.

Set PlayBook MAX_TOUCH to 4 as that seems to be all it can do.

Give it a try and see how it goes. It seems much better to me on both BB10 and PlayBook.