Add sprite atlas generation code to 2D API.

[Tape-Worm]

Add a service object that allows a user to pass in a series of GorgonSprite objects to pack onto 1 or more texture atlases. Sprites will be returned that point at the new texture(s) when done.

The object should take:

• A list of GorgonSprite objects.
• A maximum 2D texture size.
• A maximum array size.
• The resulting texture format (limited to render target formats).
• A padding so that textures won't necessarily touch each other.

When processing, this will take the sprite texture coordinates (converted to pixel coordinates), and copy that rectangle onto a destination texture. The algorithm will work similarly to the Glyph packing algorithm in GorgonFont and will try to utilize the space as best as it can. If the texture size/array size is exceeded, then a new texture should be created.

The processing method should return a data structure that contains:

1. The texture atlas(es)
2. The updated sprites.

[Tape-Worm]

Texture atlas service is now in the 3.0 branch