Plot tweaks

This makes a couple of changes to the plotting:

• The skymap is done first so that it's always done.
• The waveform plot reduced the number of waveforms it generates, this was causing memory issues.
• I added spins to the intrinsic parameter plot and redshift to the extrinsic parameter plot.

Great, does this close #99 (closed) or are there still things left to do?

I think the remaining issues are bilby issues. They are

• fixes to the waveform plots
• make plots pdfs (this is one is basically just me being picky).

Okay great, then I'll merge this and we can close that issue for now (we have an issue on bilby to fix the waveform plots).

merged

mentioned in commit 743022d5