JupyterViz grid display should be optional, since not all models use a grid or agent space

[rlskoeser]

What's the problem this feature will solve?
currently JupyterViz breaks if model.grid is not defined

Describe the solution you'd like
model.grid should continue to be optional; space should only be drawn when the model has a grid.

From testing locally, it looks like it is sufficient to modify the make_space method to check for the grid attribute and do nothing when it is defined. I'm willing to open a PR with this change if this solution is sufficient.

Additional context
Some discussion on #1772

[rht]

I can see your point, where some models don't have an explicit grid/space, but my concern is that some users might blunder by forgetting to create a space, and the explicit error/breakage helps to remind them. The other option is to have a flag that lets user explicitly disable drawing space.

[rlskoeser]

@rht that sounds fine to me; seems good to require users to explicitly opt out of displaying the space. Could you suggest a simple way to implement this? What about defining an argument for the JupyterViz space_drawer parameter that would disable it instead of getting the default display? Would False work, or is there a better way to explicitly indicate it should be disabled?

[rht]

Fixed in #1783.