Feature idea: change fast_fit options

[MNGuenther]

Instead of fast_fit=True/False and keys like secondary_eclipse and phase_curve, combine all options into one. Deprecate the old keys, and implement the new key fit_type with options

• transit: fit only the transit and mask out the rest (currently done by fast_fit=True)
• primary_eclipse: same as transit
• transit_and_occultation: fit the transit and occultation and mask out the rest (currently done by combining fast_fit=True and secondary_eclipse=True)
• primary_and_secondary_eclipse: same as transit_and_occultation
• full_lightcurve: fit the full lightcurve (currently done by fast_fit=False)
• phase_curve: like full_lightcurve but with the extra phase curve plots and calculations (could be redundant; could instead simply check if the user uses phase_curve related parameters)

[MNGuenther]

We could also use the new index_eclipses_smart for a much faster "full_lightcurve" option, as well as much faster "transit" speeds for multi-systems. The whole model fitting can be speed up by evaluating ellc only for the in-transit parts (if there is no phase_curve fit wanted). All out-of-transit parts can simply be filled with 1s.