pairinteraction

Most of the changes in this release are related to simplifying the C++ backend and do not change the python API.

• BasisAtom allow user to set mode how to use the quantum_number_standard_deviations
• backend restructure get_amplitudes, overlaps, matrix elements methods
• in C++ only define one get_matrix_elements method which can calculate matrix elements only betweeen basis objects, but allow different basis
• add the convenience methods get_amplitudes and get_overlaps only in python
• also only in python, allow to calculate matrix elements / amplitudes / overlaps between bases, states and kets (also ket atom tuples for BasisPair)
• overall in python this should now allow to calculate arbitrary amplitudes / overlaps / matrix elements between arbitrary (also different) basis, states and kets
• backend Improve BasisPairCreator with symmetries
• backend Improve database handling of column names
• backend remove unused functions get_rotator and get_ket_for_different_quantum_number_m