ICP: Seed RNG

! Seed RNG from system clock
Cloud manager: Set render output as state

+ Add a state variable for the current render_output to the cloud
  manager; it is set once a render_output is created and reset once it
  is destroyed. Now icp() does not need it as a parameter anymore (and
  generally the cloud manager should have some way to access the current
  render_output to invalidate the uniforms).
Cloud manager: Add transformation randomization

+ Add a method for rigidly randomizing all transformation matrices
  (i.e., only rotation and translation)
Lighting: Fix light direction

! The light direction does not have to be multiplied by the modelview
  matrix.