rigidbody: Add rigid body simulation

Add operators to add/remove rigid body world and objects.
Add UI scripts.

The rigid body simulation works on scene level and overrides the
position/orientation of rigid bodies when active.
It does not deform meshes or generate data so there is no modifier.

Usage:
* Add rigid body world in the scene tab
* Create a group
* Add objects to the group
* Assign group to the rigid body world
* Play animation
For convenience the rigid body tools operators in the tools panel of the 3d view
will add a world, group and add objects to the group automatically so you only have
to press one button to add/remove rigid bodies to the simulation.

Part of GSoC 2010 and 2012.
Authors: Joshua Leung (aligorith), Sergej Reich (sergof)

release/scripts/startup/bl_operators/__init__.py

@@ -35,6 +35,7 @@ _modules = (
     "object_randomize_transform",
     "object_quick_effects",
     "presets",
+    "rigidbody",
     "screen_play_rendered_anim",
     "sequencer",
     "uvcalc_follow_active",