Make check titles and namespaces translatable

[viktb]

API disruptive. Makes sense to implement with #21.

[dsnopek]

Yeah, switching to plugins would allow them to be translatable because we could use @Translation() in the annotation.

[viktb]

Exactly :)

[dsnopek]

Made an issue on D.o: https://www.drupal.org/node/2623148