rigidbody: Don't use units for spring stiffness

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54339 954f8c5b-7b00-dc11-b283-0030488c597c
rigidbody: Invert spring damping range

Before 1 was no damping, which is inconsistent with the rest of the
simulation.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54340 954f8c5b-7b00-dc11-b283-0030488c597c
rigidbody: Code cleanup

Stupid oversight, don't use floats for indices.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54341 954f8c5b-7b00-dc11-b283-0030488c597c
rigidbody: Use ARROWS empty draw type when creating constraints

Since we don't have constraint visualization yet, it's useful to see
where the individual axes point.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54342 954f8c5b-7b00-dc11-b283-0030488c597c