add OnlyGuest mixin

browser/main/Mixins/OnlyGuest.js

@@ -0,0 +1,18 @@
+var AuthStore = require('../Stores/AuthStore')
+
+var OnlyGuest = {
+  componentDidMount: function () {
+    if (AuthStore.check()) {
+      var user = AuthStore.getUser()
+      console.log(user)
+      var planet = user.Planets.length > 0 ? user.Planets[0] : null
+      if (planet == null) {
+        this.transitionTo('user', {userName: user.name})
+        return
+      }
+      this.transitionTo('dashboard', {userName: user.name, planetName: planet.name})
+    }
+  }
+}
+
+module.exports = OnlyGuest