Configure browser capabilities through YAML

[danni]

Replace code configured webdrivers with a YAML config. Replace documentation with a standard initialize call.

YAML is neat because it makes it easier to set up multiple browser configs for running your tests, especially because YAML supports inheritance, so you can do a lot of defaulting.

This branch includes some fixes for the Django steps, and the onbeforeunload fix.

[danni]

So, having looked at this in depth. It looks non-trivial to make it work without jQuery. So we can either remove it completely, or just leave it there. If you don't have jQuery, it will become a no-op because the exception will be caught and ignored..

[npilon]

See SHA: 42ebae34486eb04eb30494d41b9ecc2cfcaeb7a7 - I got fed up with not having JQuery Selectors available when writing tests using CSS selector steps, so I made a couple of utility functions to handle it. If you'd like to steal these, and incorporate them here, I think that would be a clear win.