Planette/DI: better article about autogenerated factories

On Planette, there is article about factories generated by DIC. Unfortunatelly it is bit outdated, mainly because the core example is about `Nette\Mail\Message::send()` and `setMailer()` methods, but they're deprecated since **2.1**. I propose this alternative example, but will welcome some feedback.

There should also be extra chapter about `parameters` functionality, and more detail description of the whole `create` & `implement` mechanism.

@fprochazka