fix(datepicker): adds missing iconLeft/iconRight as attributes on directive

iconLeft and iconRight on datepicker not being picked up by the directive

<input type="text" ng-model="selectedDate" bs-datepicker
      icon-left="fa fa-hand-o-left" icon-right="fa fa-hand-o-right" >

see http://plnkr.co/edit/z5KvqIrd06gvlX89994P?p=preview