Improve shifted qr solver

Merge branch 'master' of https://github.com/dune-community/dune-xt-la into try_to_fix_real_eigensolver

Pylicense update

Fix eigensolver for non-symmetric real matrices with real eigenvalues

it was missing the constuctor that takes a communicator object

Merge branch 'master' of https://github.com/dune-community/dune-xt-la into try_to_fix_real_eigensolver

# Conflicts:
#	dune/xt/la/test/eigensolver_for_real_matrix_with_real_evs_from_2d_euler_equations.tpl

real_eigenvalues() calls compute_real_eigenvectors for the checks

Refactor eigen solver