adds in tooltip for stanford only files

Uses twbs tooltip.js library (some classes slightly modified to add `sul-embed` prefix)

Closes #62

![screen shot 2014-10-17 at 3 35 21 pm](https://cloud.githubusercontent.com/assets/1656824/4687061/ea4bafea-564d-11e4-9203-1b575f0d3626.png)

The [spec](http://web.stanford.edu/~jvine/embedded-viewers/file%20viewer%20-%20simple.png) from @jvine says that the hover state should apply whenever the user is hovering anywhere in the outlined area (as well if anything is focused in that area).