Fix issue of localization messages not being found

When I tried the current development branch on my machine, it showed ??hello_en?? and ??hello_nl?? instead of the proper localised strings. Don't know if it's the dev environment (OS/versions), but this at least fixed it for me: I've added a bean to discover the message source in the resources folder.

@Lemaire Could you check whether this still works on your machine without any regressions? Marking as WIP until you have confirmed.

Closes #13 (closed)