Provide method for getting namespace from any ID

[bworrell]

IDs are QNames, which contain namespaces as part of their form. We should provide either a utility method or a new class for IDs that has a method for returning the namespace along with the ID itself.

Something like...

observable.id_.get_namespace() # returns {'namespace': 'http://example.com', 'alias': 'example'}

# OR

cybox.utils.get_id_namespace(observable.id_)  # returns {'namespace': 'http://example.com', 'alias': 'example'}

Related to STIXProject/python-stix#176