Introduced `SubsetPanel` in order to have the code reflect what is on the UI a bit more and hopefully simplify `DetailsPanelTab` somewhat (still to come).
The intention of this refactor is alos to be able to remove some of the layout hacks such as calls to `doLayout`, forced rendering and tab strip item hide/show.
DetailsPanelTab is now using SubsetPanel, which in turn 'wraps' FilterGroupPanel/AodaacPanel.
Merge pull request #817 from aodn/subset_panel

Subset panel