Make smack-android-extensions depend on smack-android

so that Users that want Smack on Android with Smack Extensions just have
to depend on smack-android-extensions.
Add message String to ConnectionException
Add MessageWithBodies and DelayedStanza Filter
Use non-deprecated method in DelayInformationManager
Ensure that Smack is initialized when calling ProviderManager
DisabledSmackClasses now also take package names

So that whole packages can be disabled.
Update flattr link in README.md