Add description, labels
Tweak some default values in Earthquake
Better random number generation

PASSINDEX is a constant of 0 unless multi-pass rendering is used,
therefore getting random numbers from the coordinate is more reliably
random.
Add Xcode project

Xcode actually does a decent job of editing GLSL shaders, even though it
can't meaninfully compile or debug them it's nice to have them in a
combined project.