Fix colormap limits for spherical viz

[cbegeman]

Colormap over/under settings from config files were not being used for spherical viz. Omega submodule is also updated.

Checklist

• Testing comment in the PR documents testing used to verify the changes

[cbegeman]

Testing

All omega-supported tests have been run on chrys with intel, openmpi

[cbegeman]

@andrewdnolan I assume that you accidentally left out the colormap over/under settings when you made the switch to mosaic. Let me know if I'm mistaken.

[andrewdnolan]

@cbegeman Thanks for catching that! Yes, in the switch from geoviews to matplotlib I must have forgotten that.

[andrewdnolan]

I'm not sure if the omega sub-module update belongs here, but I'll leave that up to you and @xylar to hash out.

In terms of the changes to polaris/viz/spherical.py, that all look good to me. Thanks for catching this!

[xylar]

Looks good to me. I'm fine with the testing you've done, @cbegeman.

[xylar]

I think it's fine to combine these things even though they're not obviously related. We can basically update the Omega submodule whenever it's convenient at this point. At some point, we'll want to be more careful about it but that's a bit off still.