Optimized Configuration, Extensions and Bundles

* Following some Matthias Noback tips, Theses classes have been improved by
overriding some magic methods to specific methods.
Beware! `self` is used here, but `static` in [line 133](https://github.com/elcodi/elcodi/pull/341/files#diff-747584c7fa484abe7c62e3ad3cae13c7R133).