Prevents materials from being duplicated after setting textures. Should fix #71 for good.

UI.cs' Awake could call toolkit.loadTextureAndPrepareForUse(); before UISpriteManager's awake had a chance to duplicate the texture, leading to said texture being shared by several toolkits
Merge pull request #151 from Crushy/master

Prevents materials from being duplicated after setting textures. Should ...