Added theme color for FxOS 2.1+

Closes #580

app/index.html

@@ -24,6 +24,7 @@
   <meta name="mobile-web-app-capable" content="yes">
   <meta name="apple-mobile-web-app-capable" content="yes">
   <meta name="apple-mobile-web-app-status-bar-style" content="black-translucent">
+  <meta name="theme-color" content="#497495">
 
   <meta property="og:title" content="Telegram Web">
   <meta property="og:url" content="http://zhukov.github.io/webogram/">