Compare DOS for integrals, not means

Merged Nathan Daelman requested to merge 1201-unstable-dos-test into develop

Updates test_dos_magnitude which compares Si DOS from VASP, FHIaims and exciting to use the integral over the occupied valence states rather than the mean. The result is a unanimous answer of 8 electrons, with deviations of up to 0.05 electron charge, instead of unintelligible values into the 1e46, where the order of deviation is much larger.

Closes #1201 (closed)

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