Verify/fix degenerate state handling.

[phockett]

Handling of degenerate states (it variable) needs some general though.

Currently:

• Select or keep it dim working OK in general, but may lead to accidental dropping or neglect of degenerate components.
• For AFBLMs using tensor formalism (see GeomFunc todo & tidy-up #26 ), may have phase issues with it>1, resulting in -ve cross-sections (or null values if summed over), although betas seem correct (only tested for N2 orb6/pig case so far). Not yet sure if this is issue in formalism (missing phase or rotation?), assumptions or numerics. Quick fix might be to just set degeneracy factor here?

[phockett]

Updates:

• Now added as degen factor (default option), or via manual selection, to AFBLMs code 2153b31
• Updated docs & added demo notebook

MF codes still need some attention, but generally not an issue for MFPADs.