Implement the Left Side folder tree for files

closes: CNVS-14717
closes: CNVS-12666

test plan:
* go to the new files page,
* on the left side there should be a tree showing
  where you are in your files.
* it should show only folders.
* you should be able to expand/collapse folders.
* you should be able to click on one of the
  folders to go to it
* it should expand automatically to show where
  you are. so if you are on
  "/courses/x/files/folder/a/b/c",
  the folders a, b and c should be expanded

Change-Id: I36b7df94423f482d44339a73549af2aa18f96333
Reviewed-on: https://gerrit.instructure.com/39094
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jason Madsen <jmadsen@instructure.com>
QA-Review: Clare Strong <clare@instructure.com>
Product-Review: Ryan Shaw <ryan@instructure.com>