Use new get_dvaluesdt, allows us to get rid of some bad code

* Get rid of ResidualSwappingExplicitTimestepper because we can just do
  the swap in get_dvaluesdt.

* Get rid of llg specific code in TR::actions_before_timestep because it
  is all handled by get_dvaluesdt.
Add command line interface for llg block solve exact/ilu in prec