Deprecate "groups" as a concept from the DataResultTree.

[jleibs]

As part of #4899 we need to update the way that the DataResultTree is presented in the UI:

• The existing notion of "Groups" goes away. Every node in the tree is an entity path and the hierarchy should match that of the tree.
  • Open design question: the group-elements in the current DataQueryResult currently have their override path set to the the recursive override root. Without the existence of selectable group-elements it's unclear how recursive overrides should be set. Recursive overrides could be a separate section of the selection panel, or a checkbox next to the different UI elements such as "apply to children".

Mock-up of future UI: