allow() and dontAllow() shouldn't run be called on a background thread

[franciscofranco]

As the title explicitly says, those callbacks shouldn't be posted on a background thread. You can either give it the option to be posted to a bg thread or simply post it on the main thread. It's slightly annoying when doing UI operations on a custom allow()/dontAllow() and then getting exceptions warning about "Only the original thread that created a view hierarchy can touch its views." and then having to wrap everything inside a main looper. At least give them the @workerthread annotation so that we know what kind of thread they're being posted on.