Provide a way to launch locally without LTI and OAuth for development/testing

[jonespm]

Semi related to #147, I think we should still have a way to develop and run locally without requiring this to be setup with ngrok and LTI/OAuth.

It's straightforward that If CANVAS_OAUTH_CLIENT_ID don't do the OAUTH check. We might need some new environment variable for LTI.

If the OAUTH check is disabled then it won't do the initial request for authorization and any actions that need OAuth (like add/remove) should probably still display but either not do anything or just toggle the UI. I'm not sure what would make automated testing for this easiest.

[jonespm]

I think this is also somewhat more related to #27. I don't think there's much point to having any of the OAuth features enabled with this. It would just display a static list.

Would still need a way to login to the admin backend.