Update netCDF Plotting

[JWiker]

Update plot_map_nc.py to do the following:

[JWiker]

@alexchartier Can you update this task with the specific updates we need?

[alexchartier]

From a website user perspective, they will select the following:
radars (in one hemisphere)
Time (you'll need to select data from the nearest minute or so)
Scatter (E, F or ground - F by default)

Then the plotting code will plot the line-of-sight velocities. Would be great if they were vectors, but colored dots might be ok too. The code is currently in plot_radar_fvel.py. I think it will need to be on a polar orthographic projection to accommodate arbitrary numbers of radars

I think the best is for the website to execute the code and then show the image. It might be good to make a timeseries of up to 12 at arbitrary spacing (anything from 1 minute to 2 hours) so we can flick back and forth on the webpage. But that doesn't have to be done inside the Python script