Change Config_MLS_SCREEN to use GetMsTicks for advancing the simulation.
Sometimes the simulation ran too fast and this change regulates the speed to
a constant.
Fix bug with cross button interference effecting highlight state.
All buttons use the same function so any static data is shared.
Fix is to fully redraw border as before optimisation but to not
always redraw the transparent text as this causes too much delay.
Change button text to always be BLACK.
Ignore highlight states when drawing the text.
Add mousex/y reset so that controls do not stay highlighted after a click that does not change screen.