Spring beans wiring, removed singletons

You could merge this pull request in separated branch, if you think so.
Spring is used just for wiring beans, I think it's not so much hard to understand. 
Now there is no need to declare a lot of singletons and useless code.

Next step I'd like to add Hibernate for ORM. This will be harder to understand for beginners.

If you have some remarks, please write and I'll try to correct it.

Thanks.