Improve IPython support

There is still more work to be done on this, but the overall goal is to improve IPython support:

* Use `width: 100%` in the notebook.
* Get rid of the need to call `initialize_notebook`. Not quite there yet, but eventually should be able to remove it entirely.
* Get rid of `.display` in favor of `IPython.display`. This already works fine.
* Get Vincent plots to "just work" on nbviewer.

Also, @wrobstory will you be at Strata this week? Would love to chat more about Vincent. If not I will actually be in PDX the following week for SIAM PP 2014 if you are around. Cheers, Brian.