Python 3 support

[Lewiscowles1986]

As the travis yaml definition states Python3 support is not there yet, lets ticket it.

This could be tiny, but it could be larger. I don't know yet

[Lewiscowles1986]

• print call -> print() call
• gdata has to go, I'm experimenting with gspread and oauth2client
• iteritems() should just be items()
• testing should use nose2 and built-in unittest at least for-now
• Pusher API client now takes extra arguments ssl and cluster
• quite a brittle structure that pre-dates blueprints and doesn't use flask.g, instead falling back on globals
• "" in "" replaced with self.assertIn() (for more helpful error messages)

Likely to be a long ride if I do get this handled, but hopefully documenting will help other interested parties.

[Lewiscowles1986]

@miguelgrinberg I hope you do not mind me tagging you on this

I have a branch that deploys and passes all tests using Python3 and newer dependencies. It removes the gdata, replacing with gspread and oauth2client, and I have tested sharing with a google user email address using that.

I may revert changes relating to Twilio client. I'm not fully sure why the Python API has so many major revisions having manually read some of the changes.

I've not taken the time to use blueprints, g instead of globals or any nicer touches or extensions of tests.