Refactor how the application is wired

[lyrixx]

Before this patch, the was many duplicated parts. There was some logic in the
GlobalHelper class, and a bit everywhere else in the application, like in the
Application, or the ContextRegistry. More over, there was too much static
call from class living in src/ to some castor's functions or GlobalHelper.

This patch clean this. Now there are DI everywhere, no more static call in our
domain!

Since the application is the heart of castor, this class hold everything!
Everything rely on DI and should stay like this.

The GlobalHelper is now a simple proxy to the application, with some convenient
methods. And it should stay like this also.

[pyrech]

So much cleaner, thanks