doesn't load so much context stuff on conversations inbox

fixes CNVS-13894

test plan
- regression test user note/faculty journal option in
 conversations compose dialog
 - be sure to try using the compose dialog as a student, an admin,
   and a teacher
 - watch for js errors in the browser developer console
- ensure that page loads faster for users with >100 enrollments

Change-Id: Ie147a3cea3e560ef8bb50adceaa6e820ef110125
Reviewed-on: https://gerrit.instructure.com/37297
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Braden Anderson <braden@instructure.com>
QA-Review: Steven Shepherd <sshepherd@instructure.com>
Product-Review: Joel Hough <joel@instructure.com>