[WIP] Notes page.

@tymofij , @olmar , @jmclaus please review.

sandbox: http://polesye.m.sandbox.edx.org/courses/edX/DemoX/Demo_Course/edxnotes
Seems docstring should be not in one line but  formatted to a multi-line docstring:
```
"""
Displays the EdxNotes page.
"""
```