[WIP] Upgrade to Capybara 2.0.
Mark some of the specs pending while I haven't found a cure.
Bump Capybara version and depend on selenium-webdriver since we're using it.
Fix pending/failing specs.

I also removed one of the image specs because response object is not
available in feature specs so this spec should probably live in
spec/requests.
Update Guardfile specifying Capybara feature spec location.
Use nicer syntax in feature spec to check if some html element is selected.
Temp solution to fix failing specs.

I've tried countless stub variations but to no avail. When these two
specs run they change I18n settings and thus cause failure in
subsequent specs which are unrelated. Still looking for proper fix...
Move recently added xhr_paging_spec under spec/features folder.