COEFF: track PCA/NMF vs. Archetypes vs. Legendre separately

[sbailey]

Currently the Redrock output COEFF column can mean different things:

• in default mode it is the PCA/NMF template coefficients
• in archetype mode, it is the archetype coefficients, and the PCA/NMF coefficients are lost
• in archetype+legendre mode some coefficients are archetype coeffs and others are legendre coeffs
  • I'm not even sure if you can tell from the output file whether it used 1+3n archetypes, or 1 archetype with 3 cameras n legendre coefficients.

I suggest that we track these separately with something like:

• COEFF is always coefficients from original PCA/NMF scan
• ARCHCOEFF (or some similar name) are optional Archetype coefficients
• LEGCOEFF are optional Legendre coefficients
  • TBD: or maybe LEGCOEFF if those apply to COEFF, and ARCHLEGCOEFF if they apply to Archetypes?
  • TBD: for LEGCOEFF[i] as the coefficients for target i:
    • if this is 1D[n], it means they are n polynomials cross-camera (like the templates);
    • if this is 2D[m,n], it means they are for m cameras and n polynomials.

@abhi0395 let's discuss and refine. Comments / ideas from others are welcome too.