Backend routing/logic for retrieving the number of plates assigned to a user

This is useful when we want only the number of plates assigned to a user i.e.
displaying the number of plates in the work list header icon.
Work list size icon

The work list size icon now updates when a user adds a plate to their
work list. Decrementing the size when a user removes a plate from their
work list still needs to be implemented.

Emit 'workListUpdated' whenever the work list size icon should be
decremented/incremented
$scope.emit('workListUpdated');
Worklist size icon karma tests