Refactor Remote and Local Backend classes.

[farmaazon]

The goal is to not write backend handlers manually, but use json schema we eventually get once cloud team configure swagger. Also we should not have too many "unimplemented" exceptions in methods.

• generate handlers for given json schema.
• split the "project management" backend API with other operations like user management.

[somebody1234]

as part of this, we could optionally port the local backend to Electron, so in the future new endpoints are easier to implement