Otto integration

See #272.

The Otto integration is a thin layer.

Here is how it works : if `@Subscribe` or `@Produce` is used on methods in an AndroidAnnotations annotated class, then these methods gets overridden in the generated subclass. AndroidAnnotations performs checks based on what Otto expects (public methods, return type, etc), and adds compile errors for faster feedback.

The overriding methods are annotated with the corresponding annotation, and delegate to super.