the second attempt to solve ARQGRA-273

* There is a big problem with testing this feature, because
  of huge differences between htmlunit and firefox drivers.
  Some tests passed on htmlunit driver, but did not on firefox
  driver.
* The second big problem is handling of staleness. When e.g.
  Actions#moveToElement() is used, the web element is serialized (somehow)
  and a command on remote driver executed. When this action throws
  StaleElementReferenceException, Graphene can't force the action
  to be performed again properly. It means that old references
  on web elements can't be cached, because the caching leads
  to staleness.