feat(carousel): expose next and prev on controller

- Expose `prev` and `next` functions on the carousel controller

Closes #4851
Closes #4853

Author: jsdevel

src/carousel/carousel.js

@@ -74,7 +74,7 @@ angular.module('ui.bootstrap.carousel', [])
     return angular.isDefined(slide.index) ? +slide.index : slides.indexOf(slide);
   };
 
-  $scope.next = function() {
+  self.next = $scope.next = function() {
     var newIndex = (self.getCurrentIndex() + 1) % slides.length;
 
     if (newIndex === 0 && $scope.noWrap()) {
@@ -85,7 +85,7 @@ angular.module('ui.bootstrap.carousel', [])
     return self.select(getSlideByIndex(newIndex), 'next');
   };
 
-  $scope.prev = function() {
+  self.prev = $scope.prev = function() {
     var newIndex = self.getCurrentIndex() - 1 < 0 ? slides.length - 1 : self.getCurrentIndex() - 1;
 
     if ($scope.noWrap() && newIndex === slides.length - 1) {

src/carousel/test/carousel.spec.js

@@ -436,6 +436,14 @@ describe('carousel', function() {
       }
     });
 
+    it('should expose .next()', function() {
+      expect(ctrl.next).toEqual(scope.next);
+    });
+
+    it('should expose .prev()', function() {
+      expect(ctrl.prev).toEqual(scope.prev);
+    });
+
     describe('addSlide', function() {
       it('should set first slide to active = true and the rest to false', function() {
         angular.forEach(ctrl.slides, function(slide, i) {