add js kaltura uploader

closes CNVS-6506

test plan:
  - enable kaltura plugin as site admin
  - enable js_kaltura_uploader on Account.default.settings
  - go to assignment that has kaltura record / upload enabled as student
  - upload a file via the RCE
    - experience should mimic existing flash uploader
    - verify that audio and video recording continue working as before
  - disable js_kaltura_uploader on Account.default.settings
  - as student attempt to upload to assignment
    - verify that it continues to work as before

Change-Id: I1f4ba5ac5df5e023f74046f33d7c623cac924ee3
Reviewed-on: https://gerrit.instructure.com/30340
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Derek DeVries <ddevries@instructure.com>
QA-Review: Myller de Araujo <myller@instructure.com>
Product-Review: Jason Madsen <jmadsen@instructure.com>