Implemented Background Scrolling Speed

Noticed that background speed settings were not added and tested Game
Maker 8.1 and found out it just modifies the background_x and background_y
just as one would assume object local x and y to work. Tested thoroughly
and all 3 graphics systems work with the fixes. Also fixed the issue so it
can only tile horizontally and not vertically and vice versa. Please merge
when ready.