shutdown your background workers!

I believe everything #74 was caused by not shutting down the userDaemon
when we do a pseudo-restart. shutdown of it and the invite daemon are
now deferred so this should fix any problems and reduce log spam.

userdaemon.go

@@ -42,6 +42,13 @@ func (rt *userDaemon) run() {
 	}
 }
 
+func (rt *userDaemon) shutdown() {
+	rt.Stopped = true
+	rt.ShutdownChannel <- "Down"
+	<-rt.ShutdownChannel
+	close(rt.ShutdownChannel)
+}
+
 func (app *appContext) checkUsers() {
 	if err := app.storage.loadUsers(); err != nil {
 		app.err.Printf("Failed to load user expiries: %v", err)