Highlight filter

This Pull Request adds a post processing filter that highlights objects in the scene.
The objects are highlighted by drawing a border around them.
The functionallity is simmilar to the glow effect. The scene is rendered using a specific 'Highlight' technique that is added to Lighting.j3md and Unshaded.j3md that renders only these objects that have to material property 'Highlighted' set to true.
In a post process, the shape edges are then extracted and drawn on the screen.
The edge color and thickness are customable.

Other highlighting effects, such as drawing the object with flipped culling again, suffer from the fact that the outline may not be drawn complete. This issue is solved by this method. However, because the scene is rendered twice and the edges have to be detected, the performance decreases. If the edge thickness is very hight, this might be a problem.

The highlight filter also does not work when mutlisampling is enabled, for some unknown reason.

Here are some screenshots from the test case:
![nohighlight](https://cloud.githubusercontent.com/assets/1770337/3787952/767a6f32-1a45-11e4-8c86-965b27aae992.jpg)
![highlight](https://cloud.githubusercontent.com/assets/1770337/3787953/7c4bd324-1a45-11e4-8ee2-438f0ed90680.jpg)