This change updates the API to use Flask Restful instead of our own
in-house REST library. This change reduces the maintenance effort and
allows us to drastically simplify the API implementation needed for the
OpenDC v2 API.

This change removes any of the user handling and endpoints from the
OpenDC API server. The API server does not need to store user
information other than an identifier in the database.

This change updates the OpenDC API to use Auth0 for API authorization.
This removes the hard dependency on Google for logging into OpenDC and
simplifies implementation as we do not have to store user information
anymore, other than the user identifier.

This change updates the project structure to become flattened.
Previously, the simulator, frontend and API each lived into their own
directory.

With this change, all modules of the project live in the top-level
directory of the repository. This should improve discoverability of
modules of the project.