rigidbody: Clean up wm notifiers in rigid body operators

Remore group notifiers, they're already sent by add/remove group operators.
Add pointcache notifiers.

Fixes UI not being updated properly in some cases.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54495 954f8c5b-7b00-dc11-b283-0030488c597c
rigidbody: Don't cancel add operator if rigid body already exists

In some cases objects might have rigid bodies but aren't in the rigid
body group, just add objects to the group then.

Also allow changing the rigid body type by using the add acive/passive
buttons. This avoids having to remove objects just to change type.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54496 954f8c5b-7b00-dc11-b283-0030488c597c
rigidbody: No need to update mass when changing rigid body type

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54497 954f8c5b-7b00-dc11-b283-0030488c597c