Drilldown query functionality.
Adding filters and (re)searching when the facet panel is clicked.
Merging state from previous root node.
Vaguely working facet panel, needs cleanup, refactor.
Updates related to integration with an actual drilldown-search enabled GeoNetwork.
Resetting hierarchical filters when necessary.
This merges @pmbohm's work whereby there's an individual component for each top level 'dimension' facet.

This is in order to get the UI looking closer to what's been specified.

Note that there are a couple of TODOs in this PR.  I intend to address them but I don't think they are enough to hold up work continuing on the hierarchical facet stuff.
Merge pull request #1361 from aodn/hierarchical_filtering_with_ui

Hierarchical filtering with ui