bug 967420

* Removed transition related app-z-level changes in zindex.css
* Cards View now hides on 'appopening' instead of 'appopen'
* Got rid of use of our own screenshotting except in the case of the
  current application where it is necessary to ensure we have one
  immediately (without having to interact with the card)
* Implemented swipe up to open card, it's sweet!
-remove MANUAL_CLOSING var, we always support manual closing via the close button and swipe-up is now for switching to the application.
-adjust treshold for showing task manager per djabber request.
Merge branch 'bug967420' of https://github.com/nullaus/gaia into 20_user_test