[2.2] [FrameworkBundle][Translation] Added logging capability to translator

Bug fix: no
Feature addition: yes
Backwards compatibility break: no
Symfony2 tests pass: yes
Fixes the following tickets: #3015
Todo: -

Adds logging capabilities to `Symfony\Bundle\FrameworkBundle\Translation\Translator`. Logging is switchable through the new `logging` config flag and defaults to `false`.

A minor addition to the Translation Component was necessary to avoid complete duplication of `trans()`and `transChoice()`.