Use webkit instead of poltergeist

Poltergeist has no support for dismissing confirm dialogs and drag and drop
seemed to fail with it. Webkit is almost a minute faster than selenium in our longest
running spec file: integration/location_page_spec

Webkit
1. 3.42
1. 3.35
1. 3.33

Selenium
1. 4.36
1. 4.22
1. 4.22