TNL-932: Add styling to Notes page.

TNL-932
@tymofij, @jmclaus, @clrux please review.

**sandbox:** http://tymofij.m.sandbox.edx.org/courses/edX/DemoX/Demo_Course/edxnotes/
@polesye In the code below, do we really need the one-liner functions ```select``` and ```close```? You could remove them and then  modify the handlers:
```
selectHandler: function (event) {
  event.preventDefault();
  if (!this.model.isActive()) {
    this.model.activate();
  }
},
 closeHandler: function (event) {
   event.preventDefault();
   event.stopPropagation();
   this.model.destroy();
},
```