Various new collectors, new component DSL and light refactoring.

- New component module - type system and a DSL for defining components
- New Darwin collector: sessions from zone
- New Darwin collector: sessions from pgrp hash
- New Darwin collectors: TTYs from sessions & zones
- New Darwin collector: user identity inference from terminal sessions
- New Darwin collector: buffers from allocation zones
- New plugin: dump_zone
- New plugin: debug_collector
- Entity classes now in rekall/entities and refactored for code health and pep8
BUG=
R=scudette@gmail.com

Review URL: https://codereview.appspot.com/151130043