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.
Personally I think this is fine; if it didn't depend on some internal state, there'd be no need for a `property`, it'd just be an attribute. It's a bit weird since it will change very frequently, but I think the only requirement for a `property` is to not take a long time to compute; this one's super fast.