Allow end assessment claim for LTI 1.3 proctoring workflow

[everythingben]

This PR makes some changes to the proctoring test workflow:

• Allow end-assessment boolean claim to be specified in the LtiStartAssessment JWT that is sent to the assessment platform.
• Return custom claim to assessment platform as part of the LtiStartAssessment JWT. This claim contains the encrypted password if the assessment requires one.
• When a proctoring request is received, route to correct view based on message type (LtiStartAssessment or LtiEndAssessment).
• When LtiEndAssessment is received, display a link to the return URL and allow addition of error/log messages.