Replace broyden2 by broyden agein until the problem with continuous restart are understood and solved

This implies the reduction of required metric calls in the broyden code path
from 4 to 2. This is now equivalent to the number of metric calls in the
old broyden code path.

This is not yet fully functional and not yet activated in the code. To activate it
the broyden call in "mix" has to be replaced by a broyden2 call.

...this surely is not yet the final version.

..also in this commit: slight cleanup in mix/metric.f90

Note: Also in this commit:

1. Changed test values in NiO_ldauXML test since now the broyden files get deleted
   when a new density matrix is generated
2. The NiO_ldau test should not work any more since linear mixing for the density
   matrix is removed for the old inp file. (It is not specified in the n_mmp_mat
   file any more)

I don't know whether there was a problem due to the absence of this code.

Note: The NiO_ldau and NiO_ldauXML tests had to be adapted to this new
behavior of the code. The new behavior is reasonable.

Up to now this is only a partial solution. There is still reading
of the n_mmp_mat file in the SCF loop to read in the optional mixing
parameters.

I couldn't identify the original bug so I did some major changes and
now everything is different.

There still is a problem but it is different now.

Note: This seems to break the LDA+U part. I commit it at this point
to get it on a computer with Valgrind available.

-removing of variable icorr, use of member-functions instead
-removal of icorrkeys module
-removal of hybridmix module
-cleanup at several places

Now fleur.F90 calls a subroutine that does most of the hybrid stuff.
In eigen.F90 only the non-local potential is added to the Hamiltonian

- do not use qfix file anymore
- do not run qfix if it is not specified in inp.xml
Fixes #96

...still very buggy.

Note: At the moment the distance in the info mode is off by one iteration.

Also in this commit: Added version info to cdn.hdf and pot.hdf

Also in this commit: Fixed a few problems due to the last
commit introducing init/checks.F90. There are still problems
remaining. The code does not compile at the moment.

Note: This functionality is not yet feature complete and
only basic usage has been tested. The cdn.hdf file will still
change.