enable boundary simulation, some tidying up

reducing some clutter by introducing logic which allows the workflow to get rid of previously necessary symlinks to prj files of certain process-subtypes. Now there are a number of allowed subprocesses (i.e. realgeometry, freezing, phaseless, sig0, nopy) and if there are corresponding prj files they will be taken, otherwise the default processes' prj file is taken. Also implemented logic to have "preinitial" boundary simulations of north and south, if a 3D realgeometry simulatiion is run. The results of these simulations are read by the pythonBCs of the 3D init and glacialcycle stage and are used as a baseline for the pressure profile at these boundaries. Therefore it was necessary to have separate BCs for north and south.