Faster Local Integration Specs

finishes https://www.pivotaltracker.com/story/show/72987724

Uses capybara-webkit for all integration specs except when testing drag and drop sortable behavior...we have to still use selenium for that. In order to use selenium, you can stub the correct ENV variable and set the driver via a tag...

```Ruby
before { stub_const("ENV", { "CI" => true }) }

it "does something using selenium", driver: selenium do
  # ...
end
```