Pack delta_x and delta_y into a single atomic.

An race condition was happening that resulted in windows moving
only horizontally on the first update, which was noticeable and
annoying.
Disable coalescing of mouse movements in events.
Use change of position of cursor instead of DeltaX/Y from event.

This fixes an issue where scrolling paste the edge of a screen will
keep moving or resizing windows.
Use real-time scheduling for worker threads.