Add select2WatchNgModel directive

- Select2 components cannot handle ng-model correctly: they do not update if the ng-model change. Add a directive to watch the ng-model and update the component value

app/assets/javascripts/admin/directives/select2_watch_model.js.coffee

@@ -0,0 +1,8 @@
+angular.module("ofn.admin").directive "select2WatchNgModel", () ->
+  restrict: 'E'
+  scope: true
+  require: "ngModel"
+  link: (scope, element, attrs, ngModel) ->
+    ngModel.$render = () ->
+      newValue = ngModel.$viewValue;
+      element.children(".select2").select2("val", newValue)