redundancies projection SC

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What has been done:

• The eigenvalue problem in calculate_eta_step subroutine is projected in the space orthogonal to the one spanned by the redundancies.
• The projected Hessian is level-shifted in case of singularities due to redundancies.
• Added test to check size-intensivity and avoid symmetry breaking of orbitals.

ToDo-list

The boxes below need to be checked before merge review will start

• Testing
  • All tests pass -rcheck flag enabled in setup.py
  • All tests pass -fbatch flag enabled in setup.py
• Versioning
  • Changelog.md is up to date
  • If merge into master: The patch number in parameters.F90 and changelog.md is up to date
• Website (Needs to be done before merge)
  • Updates (if any) to the website have been added
• Compliance with style guide
  • Do's and dont's
  • Documentation style