New tree structure with incremental addition (does not redraw whole level of a tree when things are added/removed). Currently does not work correctly for addition or removal of elements.
Merged branch 'develop' into 'feature/two-controller-tree' with conflicts resolved.
Merge branch 'develop' into feature/two-controller-tree

Conflicts:
	src/ggrc/assets/javascripts/controllers/tree_view_controller.js
Story 55768220: fixed removeChild event handler for tree view
Story 55768220: Allowing for new tree children to be added/removed without redrawing existing children
Three fixes to TreeView controller

* don't use `firstElementChild`, since it's unsupported in older but
  supported browser versions
* reduce display delay of `TreeView` by:
  - removing `options.parent` to avoid circular list references which
    cause event proliferation
  - grouping `push` and `attr` operations
* ensure `child_options` is propagated to child lists
Fix splicing in changed attribute lists
Tweaked loading animation for trees so that it doesn't go away until the entire tree is fully rendered
Merge pull request #326 from reciprocity/feature/two-controller-tree

New tree controller structure that uses a controller for each node in addition to a controller for each list of nodes (#55768220)