Fix for LDA+U linear mixing. I made a mistake when fixing #439. Switched the signs in the wrong place

I encountered a Problem where setting small negative diagonal elements back to 0 lead to much worse convergence (100 instead of 20).
Now the mixing_history is erased if we encounter a value out of the allowed bounds (Only if the density matrix is in the mixer and not mixed linearly)

...as requested by Christoph

Remove -1 for y spin offdiagonal component in greensfunction code since it was seemingly fixed by the noco changes :)

(...probably still not there, but much better)

Add version checks for new optional input parameters (Otherwise even checking if an element is there will result in a invalid xpath error)

...there are still some deviations from the expected result, though.

Hybrid

See merge request fleur/fleur!172

...not yet there.

This always had a 1.0 entry. Now it should be spin-specific in the case
of SOC. Unfortunately there still seems to be some problem as
the numbers don't add up to 1.0. But it is a first step.

Note: The storage of additional eigenvalue data can be switched of
      in the inp.xml file with the new storeEVData switch. This may
      be reasonable for calculations with many k points, e.g., when
      a highly accurate DOS is generated.