Move base64 migration prompt to corner and only when the pad is stored

customize.dist/src/less2/include/corner.less

@@ -81,6 +81,10 @@
                 line-height: 200px;
             }
         }
+        &.cp-corner-big {
+            width: 400px;
+            height: 250px;
+        }
 
         .cp-corner-actions {
             min-height: 30px;

customize.dist/translations/messages.js

@@ -222,6 +222,7 @@ define(function () {
     out.notifyRenamed = "{0} is now known as {1}";
     out.notifyLeft = "{0} has left the collaborative session";
 
+    out.ok = 'OK';
     out.okButton = 'OK (enter)';
 
     out.cancel = "Cancel";