fix assignment edit dom-ready initialization
fix assignment edit dom-ready initialization

it turns out Backbone components try to resolve their element
during initialization, not during render. so the instantiation
needs to happen inside the ready block.

the blueprint LockManager initialization also tries to
resolve a DOM component, so that needs to happen in the
ready block also

test plan:
 - /courses/X/assignments/new should load consistently

refs FOO-2597

Change-Id: I0995c227dc220e43814fbb72badf56993f2945ca
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/280925
QA-Review: Jeremy Stanley <b3f594e10a9edcf5413cf1190121d45078c62290@instructure.com>
Product-Review: Jeremy Stanley <b3f594e10a9edcf5413cf1190121d45078c62290@instructure.com>
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Charley Kline <05950d7e90ba5e3da323378368c22b3ffaaf6647@instructure.com>
Reviewed-by: Jacob Burroughs <8ecea6e385af5cf9f53123f5ca17fb5fd6a6d4b2@instructure.com>

instructure/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms