Add a /flush url to erase all stateful storage (eg. auth tokens).

Good for testing, probably.
diff --git a/app.yaml b/app.yaml
index ef69491..91482dc 100644
--- a/app.yaml
+++ b/app.yaml
@@ -14,6 +14,9 @@
 - url: /(setauth|oauth2callback)
   static_files: setauth.html
   upload: setauth.html
+- url: /flush
+  static_files: flush.html
+  upload: flush.html
 - url: /help
   static_files: help.html
   upload: help.html
diff --git a/flush.html b/flush.html
new file mode 100644
index 0000000..1949be1
--- /dev/null
+++ b/flush.html
@@ -0,0 +1,16 @@
+<!doctype html>
+<html>
+<body>
+
+<script>
+
+console.debug('flushing localStorage');
+for (var i in localStorage) {
+  delete localStorage[i];
+}
+document.write('localStorage flushed');
+
+</script>
+
+</body>
+</html>