provide simple support for dynamic subitems

Then dynamic subitems (children) can be provided like so:

`                menuItems.push({    //  added on both grids, subitems are dynamic
                    text: '<span class="glyphicon glyphicon-share-alt" aria-hidden="true"></span> Show in ...',
                    enabled: function() {
                        return $scope.jumpOptions.length > 0;
                    },
                    click: function ($itemScope) {
                        console.log ('context menu item - show details');
                    },
                    //  submenus are only supported with array model, hence '1' property
                    children:
                        $q(function (resolve) {
                            resolve(function ($itemScope) {    //  HACK: bz - dynamic subitems support
                                    return service.prepareSubItems($itemScope, jumpOptions);
                            });
                        })
                });`

Author: zoladkow

contextMenu.js

@@ -169,6 +169,10 @@ angular.module('ui.bootstrap.contextMenu', [])
                  * Regardless, passing them to `when` makes the implementation singular.
                  */
                 $q.when(nestedMenu).then(function(promisedNestedMenu) {
+                    if (angular.isFunction(promisedNestedMenu)) {
+                        //  support for dynamic subitems
+                        promisedNestedMenu = promisedNestedMenu.call($scope, $scope, event, modelValue, text, $li);
+                    }
                     var nestedParam = {
                       "$scope" : $scope,
                       "event" : ev,