Document the Lua Image widget, add UI texture resources
Allows manual atlasing of images, but doesn't resolve the issue pointed to here: #6562 as to me that issue also includes auto atlasing.
Adds a UI resource manager, which for now just has textures. I expect to use it for fonts and mouse pointers later, possibly something else I missed.
We can also change the implementation of mTexture structure and registerTexture
later to accomodate automated atlasing.
Update: don't put resolve/close anywhere near the issue or GL will close it for you automatically. :)
Edited by psi29a