"Alias" and "Envelope" modes

[skapral]

After discussion with @victornoel about envelopes here, I decided to reconsider the rule about classes left non-final and loose it a bit. Two ways (Alias and Envelope) are equally applicable for Elegant design, so the task is to introduce a configurable option for Atomizer, which can have one of two values:

• Alias - the current mode: all final classes are discarded
• Envelope - all classes are enforced to be final, unless a set of classes which are designed as envelopes. For them, the "Alias" set of rules are applied (classes non-final, methods final)

The Envelope mode also may come in handy for interoperability with envelope-designed code.