- added dragging attribute to the google-map directive
- this is important as to not rehash the functionality of "is dragging"
  that is already done in the directive controller
- this is more important that knowing if the center has changed as you
  only want to dynamically load new markers when dragging has stopped.
fixed animation bug
- delete animate was being called on the opt object when it should be
  opt.animation
- the fix is using animation, but to be consistent we might want to just
  use opt.animate everywhere.
removed the required attribute option for dragging on the google-map
directive
fixed comment for dragging attribute as optional
Merge pull request #50 from trafficland/feature/dragging_etc

- added dragging attribute to the google-map directive and animation fix