Wannier Centers in the data-file.xml

Current Wannier centers are now written-to and read-from the data-file.xml.
They are under the tag WANNIER_CENTERS.
At this time they are only tested with the cp-wf calculation using th lwf
control_flag as a determination for their execution.

Future work:
1)Further specify if the calculation is a cp-wf or a cp-wf-nscf calculation,
   both use lwf.
2)for the cp-wf-nscf calculations, write them to wfc_nscf
Plotting Wannier Functions Bug

Two small bugs were fixed in the chargedensity and the read-cards that
would not allow the Wannier Functions to be printed out while setting
calwf=1. The read_cards.f90 subroutine was also corrected, however, the
current implementation of read card PLOT_WANNIER was inconsistent with
the documentation. This was corrected as well.