Register new aliases

[fdisotto]

Hi, I've make some changes.
Now you can declare new facades with Facade::registerAliases without redeclare all preexistent facades and if you want, for example, use custom Log class you can redeclare Log alias because with my changes if alias exist replace existent class with new class.

[fdisotto]

Merge last commit, the other one is just a test that I have committed.

[itsgoingd]

Hey, sorry for the late reply, forgot about this somehow.
Thanks for your PR, but not registering default aliases when array of custom aliases is passed to the registerAliases method is a feature of the api, as sometimes you might wish to not register the default aliases (eg. In one of the legacy apps I work on there is already an App class in the global namespace). If you want to register both default and custom aliases, you can call the method multiple times, with and without the argument.