Main reason for modification is the getFlux function, which for
particular processes (ComponentTransport) relies on all solutions being
available.
This modification ripples through all of the code, especially through
the boundary conditions.
Modified `applyNaturalBC`, `preTimestep`, `integrate`, and `assemble`
functions.

Passing a vector of solutions now.

preTimestep now accepts a vector of solution together with
a process_id.
In postTimestep only the vector of solutions has been changed.

Fixes multiple copyright messages in the doxygen docu.

ag '\\file' -L --ignore=ThirdParty *Lib |xargs  sed -i 's/\(.*\)\\copyright/\1\\file\n\1\\copyright/'

Make the name schema consistent with the
implementation of other processes.

std::vector<std::size_t> _ids_of_active_elements.

MSS being the mesh subsets.

processes of HT in the local assembly.

Needed for the description of the balance data.

for flexibility in coupling.

 HTProcess::setCoupledSolutionsOfPreviousTimeStep() before use.