IP/EA-ADC up to third order

[fedy9]

• added IP/EA ADC folders like adc_pp
• extended adc_type attribute of AdcMethod to EA/IP (e.g. method.adc_type="ip"). Accessible wherever it's necessary
• IP/EA ADC matrices up to 3rd order yielding excitation energies
• added pole strengths attribute to ExcitedStates class in analogy to oscillator strengths
• IP/EA pole strengths up to 3rd order computing f amplitudes as intermediate
• added state_diffdm's and s2s transition dm's up to 2nd order for IP/EA
• new guess setup for IP/EA: appropriate estimate of guesses, symmetry setup, doubles guess construction on C++ side
• generalisation of multiple PP specific routines, e.g. the singles block is selected dynamically (p/h/ph) and no longer automatically "ph"
• New and adapted error handling
• modified 'validate_state_parameters()' function in workflow to check for valid IP/EA inputs and returns a new Boolean 'is_alpha' which is None for PP and specifies whether an alpha or beta electron is attached/detached for EA/IP. Default value is "True". Added keyword 'n_doublets' specifying the doublet states for IP/EA
• spin_change calculation was moved to utility function in guess folder
• New enforce_spin_kind routines for IP/EA
• New ChargedExcitation class with AttachedStates and DetachedStates in analogy to ExcitedStates
• added total dipole moment property in ExcitedStates for all calculations (PP/IP/EA)
• Warning for state dipole moments of IP/EA states since dipole moments of charged molecules are gauge dependent
• Modified guess setup that separates guess construction from diagonalisation of the AdcMatrix
• Updated max_spin_change evaluation in guess_zero.py to check against the actual valid values
• Updated tests and reference data generators, all tests passed
• Updated guess tests for degenerate orbital cases so CN tests run again

New methods on user side:
ip-adc{0..3}()
ea-adc{0..3}()
New keywords on user side:
n_doublets, is_alpha
e.g. ip_adc3(scf_result, n_doublets=5, is_alpha=True)
run_adc(method="ip-adc2", ...)

Remarks:

Pole strengths of 3rd order were implemented for completeness. They are currently not used in the calculation since all properties are computed at most at 2nd order even for ADC(3) calculations. Hence they were not verified yet.

No simultaneous calculation of alpha and beta states to simplify the code and error handling and to keep consistency with PP calculations. If alpha and beta would be computed in the same adcc instance, intermediates could be reused.
But they can also be reused by providing the AdcMatrix instead of the HF data

Quartets not yet implemented since they are pure doubles states which are only Hartree-Fock orbital differences.

To Do
Verify 3rd order pole strengths
Tests for state_dipole_moment of CN