Update vtkdiff submodule.

Fix a conversion warning.

Fix doxygen docu

Fix memory leaks in testrunner

This also fixes the doxygen warning for undocumented
process_id parameter

LIE_HM fix nodal aperture output

b being the aperture.
Also simplify finding the process variable id for "displacement_jump1"
variable.

Staggered scheme for coupled processes with different orders of elements

and made some other minor changes.

for flexibility in coupling.

 for the staggered coupling scheme

 in the coupling loop.

that has or overloads the member function.

for the staggered scheme.

 HTProcess::setCoupledSolutionsOfPreviousTimeStep() before use.