In the phone detail view, clicking on a thumbnail image, changes the
main phone image to be the large version of the thumbnail image.

- Define mainImageUrl model variable in the PhoneDetailCtrl and set its
  default value
- Create setImage controller method to change mainImageUrl
- Register ng:click handler for thumb images to use setImage controller
  method
- Add e2e tests for this feature
- Add css to change the mouse cursor when user points at thumnail images