Merge: Unite app.nit metadata annotations common to Android and iOS

* Rename the annotation `java_package` to `app_namespace`.
* Move up `app_name`, `app_version` and `app_namespace` and their default values from the Android platform.
* Apply these annotations in iOS too.
* Use the annotations in Hello iOS.

Pull-Request: #1233
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>

diff --cc src/compiler/abstract_compiler.nit
Simple merge