Metadata drawer subtables

[annehaley]

The metadata drawer for a region should include a subtable of associated site objects. Each site object in the subtable should be able to open a secondary metadata drawer. (At this point, we would need to conserve UI real-estate by collapsing the primary drawer).

In the secondary metadata drawer (about a site object), there can also be a subtable of associated observation objects. Each observation object should be able to open a tertiary metadata drawer.