Create separate *absolute* and *relative* retrospective tabs

[dotsdl]

From @jchodera, referring to known hack for racemic mixture handling in analysis.__init__.analyze_compound_series:

A better way to handle this (in a separate PR in future) would be to depart from what we are doing here, and instead have:

1. An absolute retrospective tab, showing predicted and experimental absolute free energies, which correctly aggregate the predicted free energy for racemic compounds (or compounds with multiple protonation/tautomeric states)
2. A relative retrospective tab, where only relative transformations between unambiguous microstates (e.g. between compounds that only possess a single microstate each) are shown

Implementation of these tabs would address the core issue the existing hack works around.