Create notification that esc can skip dialogs

If you use the shift-space combination at least 5 times per page load, a message will pop up next to the continue button stating that you can press esc to skip dialog.
![screen shot 2014-01-08 at 2 22 28 pm](https://f.cloud.github.com/assets/933422/1873091/14cc7d30-78b4-11e3-9a63-04fcfa67bdee.png)

Addresses https://github.com/codecombat/codecombat/issues/108