Handles an atlas exported from Spine. This class is created during Spine loading, and should probably never be used on its own. Code in this class is pulled from https://github.com/pixijs/pixi-spine/blob/master/src/SpineRuntime/Atlas.js
Adds a standalone image as a page and region
The name of the texture, so it can get recognized by the Spine skeleton data.
The loaded texture for the image to add.
Sets up this SpineAtlas from an instance of our TextureAtlas class to allow for the use of atlases exported from TexturePacker.