Add a flag to enable Persona support

It's disabled by default.  To enable, add the following to hydra.conf:

  enable_persona = 1

src/root/static/css/hydra.css

@@ -107,4 +107,4 @@ td.nowrap {
 
 .star:hover {
     cursor: pointer;
-}
+}

src/root/static/js/common.js

@@ -135,6 +135,7 @@ function requestJSON(args) {
             bootbox.alert("Server error: " + escapeHTML(data.responseText));
         else
             bootbox.alert("Unknown server error!");
+        if (args.postError) args.postError(data);
     };
     return $.ajax(args);
 };