chore(docs): add docs versioning

Fixes #3670
Closes #4646

misc/demo/assets/app.js

@@ -47,6 +47,12 @@ angular.module('ui.bootstrap.demo', ['ui.bootstrap', 'plunker', 'ngTouch', 'ngAn
 .controller('DownloadCtrl', DownloadCtrl);
 
 function MainCtrl($scope, $http, $document, $uibModal, orderByFilter) {
+  // Grab old version docs
+  $http.get('/versions-mapping.json')
+    .then(function(result) {
+      $scope.oldDocs = result.data;
+    });
+
   $scope.showBuildModal = function() {
     var modalInstance = $uibModal.open({
       templateUrl: 'buildModal.html',

misc/demo/index.html

@@ -50,6 +50,16 @@
                     </ul>
                 </li>
                 <li><a href="#getting_started">Getting started</a></li>
+                <li class="dropdown" uib-dropdown>
+                    <a role="button" class="dropdown-toggle" uib-dropdown-toggle>
+                        Previous docs <b class="caret"></b>
+                    </a>
+                    <ul class="dropdown-menu">
+                        <li ng-repeat="version in oldDocs">
+                            <a ng-href="{{version.url}}">{{version.version}}</a>
+                        </li>
+                    </ul>
+                </li>
             </ul>
         </nav>
         <nav class="visible-xs" uib-collapse="!isCollapsed">