[WIP] TNL-932: Add styling to Notes page.

@tymofij FYI.
@clrux FYI.

**sandbox:** http://tymofij.m.sandbox.edx.org/courses/edX/DemoX/Demo_Course/edxnotes/
> I'm going to defer to @talbs and/or @frrrances on this one.

Ah, good. Thanks.