Strip TimeDebBC.

TimeDepBC is a small modification of the behavior implemented in
PHAL::Dirichlet. Previously, TimeDepBC_Def.hpp copy/pasted all of the code in
PHAL::Dirichlet and then modified it a bit. I've stripped that out and replaced
it with an inheritance structure that uses the PHAL::Dirichlet impl. TimeTracBC
was already doing the right thing.
Note a possible bug related to PHAL::Workset::previous_time.

PHAL::Workset::previous_time seems never to be set, but
Aeras::Atmosphere_Moisture uses it and I think needs it to be changed at each
time step. Until we decide what to do, make note of it.
Modify LCM::TimeDepBC to account for a deforming mesh.

When the mesh deforms as part of reference configuration updating, the
time-dependent Dirichlet BC has to account for the moving boundary.

Right now, the modification is a kludge. A correct PHAL::Workset::previous_time
would be one way to obviate the kludge.

All behavior remains the same unless this new functionality is explicitly
invoked using
  <ParameterList name="Time Dependent DBC on NS ns_4 for DOF Y">
    <Parameter name="Mesh Deforms" type="bool" value="true"/>
  </ParameterList>