Import a bunch of stuff so users can just "from stix2.workbench import *" and
not need to import other stuff (e.g. MarkingDefinition, Cyber Observable
Object classes, etc.) from stix2.
Also remove package and module names from classes and functions.
Also remove stix2.base from docs. We hide all private classes and
functions from the docs, so the only thing the documentation for base
included was STIXJSONEncoder.
Chris Lenk