New mechanism of scroller data custom processing (with usage sample)

A new parametr 'processing' is introduced. It's a name of object in ctrl wich will get insert-update-delete methods after ui-scroll compiles.

See the demo http://rawgit.com/dhilt/NGScroller/insert-update-delete/src/examples/twoUpdatableLists.html of two scroller lists wich are using the same datasource and the different processing objects.

A minimal changes with backward compatibility.