Merge pull request
#2175 from minrk/staticfile
add FileFindHandler for Notebook static files
* The static file handler now uses a search path, instead of a single dir.
This allows easier customization of available js/css,
and provides a place for extra files to go for extending the notebook.
* An empty custom.js / custom.css are added to the templates for trivial
custom user styling/scripting.
The search only happens once, and the result is cached after the first.
* A few methods are pulled from tornado 2.2-dev verbatim to have tornado 2.1 compatibility.
* mathjax is now installed by default in profile.
