Think about how to deal with "difficult" dependencies in the metapackage

[adamltyson]

It's likely that some depenencies will be incompatible, especially for fetching & visualising different types of anatomy data for brainrender(napari). We should work out what the best way of dealing with these are, e.g.:

• Only allow compatible dependencies
• Install with brainrender[streamlines] and brainrender[geneexpression]