[SPINE] Updated to latest version + added skinned mesh attachment support.

This is a pretty big change to the spine components but self explanatory:

- Separates the Spine.js file into two files
    - Spine.js which contains the raw spine runtime directly from esoteric software (the needed changes for pixi.js were merged into the main branch https://github.com/EsotericSoftware/spine-runtimes/pull/315)
    - PIXISpine.js implements the pixi.js specific details about how to load and draw spine animations. This new implementation supports region attachments and skinned mesh attachments.
- JsonLoader implements the new loading system required by Spine 2.0 files (free update to spine users)
- Adds the ability to select between drawing GL_TRIANGLE_STRIP or GL_TRIANGLES buffers to Strip.js, after this change it feels like "Mesh" would be a better name for the class. Also uses the padding variable when rendering in canvas rather than WebGL.

Adding more attachment types at this stage is trivial, I will add them as I need them. Here's an example; these are two sprites animated using skinned mesh attachments (rendered with pixi.js in safari with WebGL enabled):
![](http://i.giphy.com/5xaOcLtf6Ch5nkkjcic.gif)