Remove glsl-unit

Unfortunately, the [glsl-unit](code.google.com/p/glsl-unit/) project (a GLSL minifier and templating system) seems to be dead. There are a number of outstanding bugs, the project has not been touched for a year and a half, and the original developer has moved on. The generated output is incompatible with IE11 (see #1051).

This PR adds a simple drop-in replacement for glsl-unit. It preserves the templating system (useful) and does simple minification, which works as well as GLSL unit for our simple shaders.