[MNT] - Make grid an updateable argument in PSD plots

[TomDonoghue]

Minor update to managing style of PSD plots to allow for passing in and controlling whether there is a grid or not.

[ryanhammonds]

Looks good! The only thing I could think of is if grid could be doc'ed in the plot_spectra docstring under **plot_kwargs or maybe the .plot method where plots are usually called from? Otherwise it may get hidden away / user may not know about since it's unlikely to call style_spectrum_plot directly.

[TomDonoghue]

Hey @ryanhammonds - yeh, I agree that a limitation / issue with our general strategy for applying plot style is a bit opaque, including for knowing what can be passed in. To try improve that, following your suggestion, I updated the docs in the spectra to mark the special-case of passing in grid, and also did a sweep through to try and better describe how plot_style works, and update the mentions of this across the board - can you take a quick check of the new updates and see if this seems better? I also extended the settable axis plot kwargs (following from NDSP - neurodsp-tools/neurodsp#319)

[TomDonoghue]

Going to merge this one in now to prepare a new release candidate!