Fix bug in RelatedObjects
Take apply_condition out of dictionary representations when the value is not a list
Add ReceivedLine class and round trip test.
Clean up some property tests
Clean up controlled vocab tests
Add ReceivedLineList type

Also make EntityList much more generic, to define the default behavior
of (to|from)_(obj|list) functions.
Update EmailHeader for 2.0
Add Reference types (used for Attachments and Links on Email)
Add simple_email_pattern example
Make recipient lists a bit easier to use
Make relationship into a ControlledVocab string
Fix creating obserservable out of ObjectProperties that already have a parent Object
Lists of strings are now valid to pass to EmailRecipients.__init__, but not a list of ints
Merge remote-tracking branch 'origin/cybox2.0' into cybox2.0