Output correctly-timed waveforms

[jacopok]

Currently, waveforms are output with a shift in time compared to their EOB counterparts.
This was acceptable in earlier versions of the software, but it is not anymore, since we are trying to build a combined inspiral-postmerger model by hybridizing with NRPMw.

The approach is as follows: instead of computing the residuals in phase and flattening them by an arbitrary amount,
we almost flatten them by shifting the waveforms by an amount determined by a fit to the timeshifts at hand,
which was done by Matteo here.

So, the steps to take are:

• include the time shift by the fit amount both in the generation of the training dataset (removing the flattening) and in the reconstruction
• include the fit in mlgw-bns (function ParamsWithExtrinsic -> float)
• test it
• remove the possibility to shift in time when computing mismatches from existing tests (expecting a failure)