TNL-731: Add possibility to search notes.

**Ticket:** [TNL-731](https://openedx.atlassian.net/browse/TNL-731)
**sandbox:** http://tymofij.m.sandbox.edx.org/courses/edX/DemoX/Demo_Course/edxnotes/

@explorerleslie,
@tymofij , @olmar , @jmclaus please review.
> What is the purpose of this underscoreJS bindAll with no method names at all? In the doc, it says that the second argument is required.

@jmclaus it was possible previously. See http://underscorejs.org/#1.5.0