glview: Implement 2D orthographic view

- Add GLView2D class; visualises 2D via orthographic projection
- Image planes are demand-loaded
- Add 2D vertex and fragment shaders
- First three UI sliders (x y and z rotation) are now non-functional
- Last slider navigates z planes; this will be accompanied by visual feedback on the terminal

![glview2d](https://f.cloud.github.com/assets/1528953/2506798/e897a340-b3ad-11e3-8648-6a57f23366f3.png)