Have Collage texture pages grow dynamically as needed

[tabularelf]

Right now all Collage texture pages are always set to their absolute maximum size. This is great for adding a bunch of images at once, but that also means that memory is almost always higher than it should be.

This change would inherit some logic from Canvas (another library of mine) that will allow it to resize the underlying surface, while maintaining the existing contents. This will however likely break HTML5 compatibility.