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.

This change reduces the trace sampling rate of the Sentry SDK to prevent
reaching the limits of the free Sentry subscription.

This change removes the `api` prefix required by the API server in the
path, given that we have started to host the API on its own domain
(api.opendc.org) and thus does not need a prefix.

This change enables CORS for non-local deployment in order to allow
other domains to make requests from the browser to the OpenDC API.

This change makes the frontend independent of the API by removing the
static file serving logic from the API server. Instead, we can serve the
frontend as static HTML over CDNs.

This change renames the web-server component to API in order to be more
descriptive of its role. The OpenDC API bridges between the frontend on
one side and the database and simulator on the other side.