Key overlay

[yugecin]

Notes

• osu! adds a text shadow, I couldn't find a decent way to do this (I commented a method to do this). This shadow is very useful when the text is colored white.
• I'm not sure how to correctly position/scale the background, it does not show correctly with some skins.

[itdelatrisu]

Thanks as usual, looks great! But you forgot to commit the images. 😛

I'd prefer the InputOverlayKey class to go in a separate file (perhaps in itdelatrisu.opsu.ui) since Game.java is already way too long.

[yugecin]

Whoops, added them (yugecin's law again >.<)
I also thought it should be in a separate file, but didn't know where to put it. Moved it now.

[itdelatrisu]

Awesome, thanks! :)