handle showing all possible contexts in newfiles

closes: CNVS-15265 CNVS-12729

test plan:
* enable better_file_browsing feature on the account
you belong to.
* go to '/files'
* it should look like this: http://cl.ly/image/0q3R1m0j2x0F
  and all work

fixes: CNVS-15409
* try moving a file, it should only let you move
  it to stuff in the context it came from

Change-Id: I3b4c892220e78ddbe2ac074b036914535e06303d
Reviewed-on: https://gerrit.instructure.com/41410
Reviewed-by: Jason Madsen <jmadsen@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Ryan Shaw <ryan@instructure.com>
QA-Review: Ryan Shaw <ryan@instructure.com>