This is like what we have to DI and classes, but for callables.
The motivating factor is to get rid of *service locators* in the `boot`
method of apps as a new pattern is about to emerge where we have lots of
`query` calls on the app or server container in order to fetch some
services.
With this little helper it's possible to call another (public) method
and magically have everything injected.
Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>
4a3ea04baa