[feature] Changed scope of getTranslationMessages to protected

I changed the scope of the function getTranslationMessages to protected.

# Scenario
I don't want to dump all my translation files/domains to the web/js directory. I've created my own *TranslationDumper* class that inherits from *Bazinga\ExposeTranslationBundle\Dumper\TranslationDumper*. 
I would like to override the *getTranslationMessages()* only so I can benefit form possible future bugfixes/features in the rest of the *Bazinga\ExposeTranslationBundle\Dumper\TranslationDumper*-class.