Removed all global $(document).unbind calls from interactive

Summary:
We often use $(document).bind to handle movement events that occur after clicking on an
element but moving the mouse outside of it, later $(document).unbinding these events in a way that
could remove other events bound to the document. jQuery allows you to namespace events, which I've
added, e.g.: $(document).bind("vmousemove.polygon vmouseup.polygon"), which can then be removed with:
$(document).unbind(".polygon").

Test Plan:
- Run Perseus.
- Create an interactive graph.
- Play with: (1) line segment, (2) polygon, (3) the points on the polygon.
    - Check that they hover when moused over, unhover when mouse outed, etc.
    - Behavior should be identical to master.
- You should also open khan-exercises and try an exercise like "Ordering Fractions".
    - Check that the sorter works as expected.
- To make sure that additional events weren't being unbound, I also added an extra event to vmousemove
  and checked that it remained bound. See the attached GIF.

Reviewers: jack

Reviewed By: jack

Differential Revision: http://phabricator.khanacademy.org/D10650