Declarative Plotting Tab Completion

[jrleeman]

We need some enhanced discover-ability for the declarative plotting interface. In JupyterLab pressing tab on an instance of an ImagePlot or similar produces nothing, which is unfortunate for the user.

[dopplershift]

I just tried and didn't get back nothing:

Might still be nice to use the hooks to hide the less-useful attributes, since the declarative interface is focused on simplicity.