[WIP] Notes page.

@tymofij , @olmar , @jmclaus please review.

sandbox: http://polesye.m.sandbox.edx.org/courses/edX/DemoX/Demo_Course/edxnotes
> What do you think about this formatting?
> 
> self.assertItemsEqual(
>     [self._get_dummy_note(self.html_module_1, self.vertical)], 
>     json.loads(helpers.get_notes(self.user, self.course))
> )

Agree. Fixed.