Dynamic Input Textures specification 2

[iwubcode]

Very early implementation of the 2nd iteration of dynamic input textures.

This aims to fix the following problems:

• Game UI icons that represent the same button but with different styles (ex: an "A" button pressed vs an "A" button front-facing)
• Game UI icons that represent multiple buttons (ex: a dpad icon)
• Game UI icons that have coloring or art behind the icon, where we'd prefer to overlay the new icon
• Regions that exist outside the image bounds will be cut off

There may be more features added too.

The new spec is unfortunately not backwards compatible (though Dolphin will still read the original spec as well). In my infinite wisdom I didn't really plan ahead very well :)

The new spec should be ok moving forward though. It's based around the idea that there are various bind-types and each one has different properties. This will allow us to add new bind types or new properties in the future.