Show inventory outlines in single dataset view.

[jmalczyk]

To tease out inventories behind grid-based counts.

[villanueval]

Depends on MapofLife/database#321

[jmalczyk]

For single inventories that would work, but for multi-site inventories the dataset coverage polygon is going to be the union of all polygons it contains. For here I think we want to see the outline of all those individual polygons that a dataset might contain. So for dataset that contains many parks and protected areas within a larger region (which may overlap) we would see all those outlines broken out.