Cleanup and Refactor Editor.py (API Doc) for Scribes 0.4

Editor.py is the API. Thus it should be free from implementation details and unnecessary artifacts. Developers should open this file and be presented with APIs (attributes and methods) they can use to extend Scribes via plugins. This has several benefits:

1) Developers don't need to care or worry about implementation details and can instead focus on doing stuff (writing plugins).
2) Developers don't need to worry about organization and structure of the Scribes core (mainly boring tedious stuff).
3) Developers have a single API to study (that is the editor object).
4) Developers don't need to browse the interweb looking for documentation, Editor.py is basic documentation.

WHAT TODO:
===========

- Remove all services and initialize them in a separate module (except the Class that initializes all the services)
- Remove private attributes
- Remove private methods
- Remove signal definitions
- Remove signal connections
- All signals should be defined AND DOCUMENTED in SIGNALS.py (Editor.py extends it)
- All attributes and methods in this file should be public API only
- Editor states should be managed by specialized modules (preferrably, one module per state)
- Destruction of the editor will done by the a RegistrationManager object.

That's it!