code: function (e) {
              if (this.dragging === false) {
                  this.dragging = true;
                  this.grabOffset.set(e.gameX, e.gameY);
                  this.grabOffset.sub(this.pos);
                  return false;
              }
          }
docs: Gets called when the user starts dragging the entity
  @name dragStart
  @memberOf me.DraggableEntity
  @function
  @param {Object} x the pointer event