Fixes compilation and post email issues

Hi Ole,

I came across your blog post on RACCommandExample this morning and it is really cool! Thanks for posting it. I tried your sample and found this 2 issues on this request.

There was a compilation error due to the **DCIntrospect.h** import in `AppDelegate.m`.

Another issue was that the email was not being sent when user tapped *Subscribe*.
Just moved some code around in `SubscribeViewModel.m` to get that working.