ToC does not update on cell execution

[dacoex]

When entering a heading and executing the cell, the ToC is not updated.

Only after re-enabling the ToC via the button in the toolbar.

[jankatins]

Have a look at #44, which adds a reload button (no auto reload though :-( )

[jankatins]

JFYI: the toc included in the ipython-extension repo has now auto-update: https://github.com/ipython-contrib/IPython-notebook-extensions/blob/master/nbextensions/usability/toc/main.js#L151