rigidbody: Add "Apply Transformation" button

This is just the "Apply Visual Transform" operator.
It's very usefull for rigid body simulations but hard to find and users
usually don't know about it/don't know it's usefull to apply rigid body
transformations.
It seems bit out of place (especially the tooltip) so we might need to
do a bit more here.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk@60929 954f8c5b-7b00-dc11-b283-0030488c597c