Adds 'immutable' option to draggable

This option keeps the original items in the draggable list, allowing
dragging and dropping the same element multiple times.
Adds the 'keep' option to placeholder

The keep option to the placeholder argument
keeps the draggable immutable
Returns the dragItem to the onDrop function

This change returns the dragItem to the onDrop
function. This allows manipulation of the object
that is dragged directly.
Merge pull request #8 from bbonamin/immutable

Updates 'placeholder' option to draggable
Remove immutable option and update shopping cart demo
Merge pull request #12 from bbonamin/master

Returns the dragItem to the onDrop function
Fix bug arises because of placeholder=keep option
Merge pull request #14 from wesleycho/master
clean up
tests fail
Test ngDragDropService
nested ng-model failure test
indentation corrected
Fixed failing test: should move item from foo.list1[0]:placeholderTrue to foo.list2[0]:dummy
Merge pull request #17 from finalclass/master

Allow drag and drop for nested models
Evaluate draggable model in source scope
Merge pull request #20 from tp7ptr/master

Fix for multi scoped draggable/droppable e.g. dragging an item from Controller 1 to Controller 2.