Specific actions if DoubleTap on a known element

DoubleTap in empty space will zoom like before
DoubleTap on an image will save it
DoubleTap on a link will open it in a new background Tab
(Configure in Settings => Advanced => Double Tap Contextual Mode)

Change-Id: I2cfaa2ae81f2814c68c2c3b8d70a3220e594677a