Implement simple spellchecker

src/common/settings.js

@@ -23,7 +23,9 @@ function loadDefault(version) {
       notifications: {
         flashWindow: 0 // 0 = flash never, 1 = only when idle (after 10 seconds), 2 = always
       },
-      showUnreadBadge: true
+      showUnreadBadge: true,
+      useSpellChecker: false,
+      spellCheckerLocale: 'en-US'
     };
   default:
     return {};