add german language translation

- add langs/de-de.js
- modified config.js and config-default.js to add new language to selector

public/config-default.js

@@ -15,6 +15,10 @@ var Config = {
             "filename": "en-us",
             "name": "English"
         },
+        {
+            "filename": "de-de",
+            "name": "Deutsch"
+        },
         {
             "filename": "zh-cn",
             "name": "简体中文"
@@ -30,4 +34,4 @@ var Config = {
     ],
     "lang": "en-us",
     "theme": ""
-};
+};