Expose phase coefficients in TaylorF2 internals

This merge request contains two features:

• First, and hopefully, uncontroversial: It makes no sense that the tidal terms in TaylorF2 are set outside of the XLALSimInspiralPNPhasing_F2 function. Everything else is set in there (e.g. self-spin terms, non GR stuff). This patch moves the tidal terms internally to this function, and fixes a helper function that was currently working around this.
• Second, and potentially more controversial: I want to expose the F2 phasing coefficients (to python, as well as C), so that a user can generate the phasing coefficients, edit them and then generate a TaylorF2 waveform with the edited coefficients. I see a few use cases for this: First is that it makes it easier for waveform experts to edit the phase coefficients and turn stuff on and off, second is that the testing GR stuff might be a bit easier if one could just edit stuff directly, third (and my own use case) is for the case of computing F2 Fisher matrices, one wants to perturb the F2 coefficients slightly and measure the match. The code to do this last will be put in PyCBC's tmpltbank module, but will require this change.

This will certainly require discussion on the waveform call. This does not edit waveforms generated from ChooseTD or ChooseFD and friends. Only the PE code seemed to be not calling F2 in this way, and I will patch that use case here. (Note: I have not yet done that, pending discussion on the above, but the patch is simple and can be done without anyone from PE needing to worry (or even know) about this change!)