update showndown to 1.9.1

this has openLinksInNewWindow which is smart enough that internal links
open in same tab and external links open in new tab

src/js/setupaccount.js

@@ -7,10 +7,10 @@ var app = angular.module('Application', []);
 
 app.filter('markdown2html', function () {
     var converter = new showdown.Converter({
-        extensions: [ 'targetblank' ],
         simplifiedAutoLink: true,
         strikethrough: true,
-        tables: true
+        tables: true,
+        openLinksInNewWindow: true
     });
 
     return function (text) {