add release version to all API responses

[rahulbot]

We have an informal standard of returning a services release number in every response, typically via a decorator used on all endpoints. This required us to have a central VERSION constant to track the app version, and return something like:

{ 
    "version": "v0.1.1",
    .....
}

(associated with #2)

[rahulbot]

Note: the API version is actually returned in the response header: ('x-api-version', '1.0.0') This doesn't match our standard, but is a place it can be retrieved.

[rahulbot]

Closing since this has a solution already (in the header)