Animation fix FF + new easing functions

Added 3 new easing functions (inspired by http://www.w3schools.com/cssref/css3_pr_transition-timing-function.asp ).
Fixed the issue about animation of backgroundPositionX and backgroundPositionY on FF ( http://stackoverflow.com/questions/13948617/backgroundpositionx-not-working-on-firefox ).

At the moment it works only when the start value is 0, because the aria.utils.Dom.getStyle() method returns wrong value for FF  ( https://github.com/ariatemplates/ariatemplates/issues/744 )