wait for mask to disapear on big pages

In order to avoid this kind of error :
An error occurred in an after hook
  Capybara::Poltergeist::MouseEventFailed: Firing a click at co-ordinates [1037, 20] failed. Poltergeist detected another element with CSS selector 'html body form div.controls div.chooser-container div.chooser-mask' at this position. It may be overlapping the element you are trying to interact with. If you don't care about overlapping elements, try using node.trigger('click').
add find args like match
Merge pull request #1 from akarzim/master

accept options like :match for find method