Fancy progress

This PR implements fancy progress tracking:

* Progress bar will automatically be shown if the ETA is more than a second.
* Progress will be displayed visually as a bar and also as a percentage number.
* The progress bar displays the ETA (estimated time of arrival). (Though, I'm using the simplest possible formula to calculate it right now.)
* The progress bar will display how long the simulation took after finishing.
* The width of the progress bar adjusts to the terminal width if Python >= 3.3 is used (otherwise it defaults to 80 characters)
* In an IPython notebook a fancy HTML/Javascript progress bar will be rendered.

This PR is an alternative suggestion to PR #476.
In an event-driven language, I would make a timer object that calls this function every `update_interval` seconds. Is [`threading.Timer`](https://docs.python.org/2/library/threading.html#threading.Timer) analagous? See also [`sched`](https://docs.python.org/2/library/sched.html).