now works on a per-element basis and has been moved to the local rod assembler.
That way, it has lost most of its 1d-ness.  In the future, it will be usable
for other problems as well.

[[Imported from SVN: r4019]]

[[Imported from SVN: r4016]]

The class 'Configuration' is now called 'RigidBodyMotion', and can be parametrized by the space dimension

[[Imported from SVN: r4003]]

[[Imported from SVN: r4001]]