Add media queries and mobile viewport

res/welcome.html

@@ -158,6 +158,16 @@ we don't have an account and should hide them. No account == no guest account ei
     display: none;
 }
 
+@media only screen and (max-width : 480px) {
+  .mx_ButtonRow {
+    flex-direction: column;
+  }
+
+  .mx_ButtonRow > * {
+      margin: 0 0 10px 0;
+  }
+}
+
 </style>
 
 <div class="mx_Parent">

src/vector/index.html

@@ -15,6 +15,7 @@
     <link rel="manifest" href="manifest.json">
     <meta name="referrer" content="no-referrer">
     <link rel="shortcut icon" href="<%= require('../../res/vector-icons/favicon.ico') %>">
+    <meta name="viewport" content="width=device-width, initial-scale=1">
     <meta name="apple-mobile-web-app-title" content="Riot">
     <meta name="application-name" content="Riot">
     <meta name="msapplication-TileColor" content="#da532c">