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.
It gets incremented (`self.steps + n`), but is prevented from exceeding `max_steps` which would give a progress of more than 100%. Do you prefer to ensure that when returning the progress instead of during the increment?