Web-based progress bar.

This pull request is very much a proof of concept for a weekend hack, but I thought it might be of interest at least for discussion. As such, the code is decidedly a mess still (notably, I've not yet tried to get it working under Python 3). At any rate, this PR adds a new subclass of ``BaseProgressBar`` that uploads status monitoring information to a small web app that I started, [tskmon](https://tskmon.herokuapp.com) (also a mess). A screenshot of this in use by one of the GRAPE notebooks can be found [here](http://imgur.com/6xBt4Ic).

The idea for this functionality is to make it easier to remotely monitor long computations from a phone or tablet, without having to worry about SSHing to a server. If you find this interesting, let me know, and I can try to start cleaning some things up as a spare-time project. Thanks!