Refactor and fix NRSur7dq2 for waveform review
The NRSur7dq2 waveform review (https://git.ligo.org/waveforms/reviews/nrsur/wikis/home) is wrapping up and the code changes have been completed. This refactors the NRSur7dq2 code into utilities that will be useful for future NR surrogates and the NRSur7dq2-specific waveform generation routines. It also fixes several bugs uncovered, and updates waveform conventions to align with those of lalsimulation.