WIP: Add binary black hole waveform generator
This MR adds a subclass of the WaveformGenerator
which is specifically for binary black holes.
This means the user doesn't have to specify the source model, or the function to convert parameters.
I updated the GW examples to use this where appropriate.
@paul-lasky @gregory.ashton @moritz.huebner is this a useful new feature.
Edited by Colm Talbot