This change creates a new lms/cms endpoint which accepts unauthenticated
requests to securely create zendesk tickets. This allows javascript code to
create tickets without exposing ZENDESK_OAUTH_ACCESS_TOKEN

EDUCATOR-1889

In particular, implement a validation API for registration,
where a client makes AJAX calls to the endpoints requesting
validation decisions on each input. Responses are strings
dependent on the type of validation error; if no error,
then empty string to indicate OK.