Colladaloader kinematics

This adds support to the ColladaLoader to parse kinematic information out of collada files and move individual joints around. I'm using it to do cool things with robots. I wrote an example of you can check out on my fork [here](http://stonelinks.github.io/three.js/examples/#webgl_loader_collada_kinematics).

Basically what I've done is have the collada loader export a `kinematics` data structure with the following properties:

#### `joints`
An array of `joint` instances with data parsed out of collada. Joints can be either prismatic or rotational, and contain information about their min / max limits, axis, zero position, etc.

#### `setJointValue( jointIndex, value )`
Move a joint at the index to a particular value

#### `getJointValue( jointIndex )`
Get a joint at the index

Let me know if you see any issues and I'll be happy to resolve them. I tried in particular to work within the existing infrastructure of the collada loader and follow your coding style.

Thanks!