To be fair, it was more on the level of entire functions using different
indentation than the surrounding code, but it's not consistent enough
for me to justify leaving it alone.
This makes the "[Press ENTER to return to editor]" fade out after a few frames, allowing screenshots of custom levels to be cleaner and to make sure nothing is obscured while the user is editing their level.
This commit also adds alpha support in BlitSurfaceColoured, where it takes into account the alpha of the pixel *and* the alpha of the color.
`graphics::getRGBA(r,g,b,a)` was added to help with this.