Initialize data subscription without a data-controller

[Raphael]

Description

Since in the very basic data-controller it is mostly just an empty abstract extension. So this could be fast forwarded to have a controller automatically initialized, when no controller is given by default.

Something like:

import { DataSignature } from 'gluebert/data';

const SIGNATURE = new DataSignature('key.data');

export {
    SIGNATURE,
};

should become a valid data observable to key.data