[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?
```python
self.assertItemsEqual(
    [self._get_dummy_note(self.html_module_1, self.vertical)], 
    json.loads(helpers.get_notes(self.user, self.course))
)
```