add a kaltura plugin option to hide RTE record icon

As an intermediate step to making the canvas video integration
more extensible, this allows the video button to be hidden
in the RTE but not in the other areas that you can record
video in: conversations, SpeedGrader, Media Recordings homework
submissions.

Test Plan:
 * Enable the kaltura plugin option to "Hide the video icon in the RTE"
 * The video icon should not show up in any RTE
 * Video recording should still work in conversations, SpeedGrader,
   and as homework submissions. (but not in "text" homework submissions)

closes CNVS-12040

Change-Id: Ib2599e2248d9931df006da8ec1deec85eb050751
Reviewed-on: https://gerrit.instructure.com/32010
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
QA-Review: Nathan Rogowski <nathan@instructure.com>
Product-Review: Bracken Mosbacker <bracken@instructure.com>