Put Sprites in a Shared Assets SWF for easy skinning

[alexsylex]

For modders that want to make their own skins. Separate the scaleform part into two:

• The control logic. Can be updated, correcting bugs without forcing the modders to rebuild their version for the assets to work.
• The assets file, containing the sprites, that the modders have to update only in case a new sprite is added.