new roles

refactor everything that used to use strings for roles
to use actual role_ids

the apis should be backwards compatible so we don't need
to update (most of) the UI's right away in this commit

test plan:
* regression tests for permissions, role overrides,
 alerts (for account roles), enrolling users,
 adding account admins, etc.

refs #CNVS-15481

Change-Id: Id57fd3104c5c518b6fbf180609950dcddcdd474d
Reviewed-on: https://gerrit.instructure.com/41208
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>
QA-Review: Steven Shepherd <sshepherd@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>