Vgen refactoring finished

See merge request fleur/fleur!2

+make io/eig66_mem.F90 read_eig capable to read only certain bands

# Conflicts:
#   init/initParallelProcesses.F90
#   init/old_inp/fleur_init_old.F90
#   main/fleur_init.F90
#   vgen/mpmom.F90

The old test is renamed to SiFilmPlotXML.

+ bugfix for density slice generation in main/cdngen.F90

This is a preparation to allow the explicit choice of the bands to be
included.

+ some changes of code order

+ some minor cleanups.

1. This fixes the problem from the previous commit.
2. Also in this commit: move qmat array to cdn/qal_21.f90 as it is used nowhere else.

Note: This cleanup includes the inclusion of the qvlay array
into the t_regionCharges type. This breaks the program logic
for the noco%l_noco case as it is created inside a certain
spin loop but should be created outside this loop. It is not
yet clear how this will be solved. Probably the regCharges
type should just move to cdngen and the arrays in it should
have full spin dimensions.

...bugfix for debug mode as suggested by Daniel.