Lump metrics in analysis by their same parent folders in the QRIS tree

[Jdgilby]

Right now all metrics get dumped into the table in a random manner. My suggestion is to add headers and group metrics by their different categories. This would make it much easier to find the metric you are after, especially with the long list we have. The headers could potentially be automatically collapsed if we wanted.

[KellyMWhitehead]

Just for my future reference: https://stackoverflow.com/questions/54385437/how-can-i-make-a-table-that-can-collapse-its-rows-into-categories-in-qt