add UI tabs
* ng-click sets the value for tab
* ng-init defaults the value for tab to 1
* ng-class adds a class to an element depending on the value of tab
* ng-show toggles the tabbed area depending on the value of tab
change tab handling into a controller
* default via value assignment in controller
* selectTab to change the value
* isSelected to ask what's the value
add more data
add gallery controller
* $index contains the number of the iterator
* ng-click handler to switch between the product images