plotbase.plot_phased_mag_series: add model option

[lgbouma]

looks like the following if you use it

[waqasbhatti]

Thanks, this is pretty awesome!

Minor comment on the linewidth of the model plot: let's make this linewidth=2 or so instead of linewidth=1 so it's a bit more prominent.

Also, I'll take advantage of you working on this file already to ask if you mind adding a plot_phased_magseries function wrapper in plotbase.py that just calls plot_phased_mag_series with all the same args. This will make it mirror the lcfit.[fitype]_fit_magseries functions and makes for a bit more fluent API.

[lgbouma]

done, see pic

[waqasbhatti]

Awesome, thanks again!