Fix return value for DatafeedBase.parse

Any subclass that calls self.parse() should expect two return values.
Add documentation for notification types
Merge pull request #1102 from mc10/tests

Fix return value for DatafeedBase.parse
diabled FMS datafeed tests. FIRST pages currently don't work
Merge pull request #1106 from phil-lopreiato/webhook_docs

Notification Structure Documentation
Merge branch 'master' into gcm_broadcast