Diagonalization of the photo-absortpion tensor

It modify some output format for the case the sigma is diagonalized. It fix some problem in the diagonalization procedure that gives LAPACK errors. "* In deigensolve_nonh, LAPACK dgeev workspace query returned error message 32521"

It introduce a new variable PropagationSpectrumSymmetrizeSigma. Photo-absorption cross-section tensor should be symmetric. This variables ensure that removing numerical fluctuation.

Checklist

• I have checked that my code follows the Octopus coding standards
• [] I have added tests for all the new features added in this request.

added 2 commits

• f917418d - Removing i
• 01231e71 - Reformatting if statment

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changed milestone to %9.0

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merged

mentioned in commit c84b7a2e