Consider scripting integration with the napari console

[gselzer]

In #265, @kephale added a widget that replicates the Script Interpreter in napari-imagej. However we noted on Zulip that ideally, we wouldn't need to add a second console - we could access all of the desired variables through the napari/napari-console plugin that currently exists.

I'm not sure whether this functionality is currently possible though, so I haven't implemented it yet.