Default domain settings

Idea behind this pull request is to be able to define different default domain.

We are creating different domains for different parts of the system to translate these separately. Now we can define default-domain which should be used for all translations which are not using different domain explicitly.

Does it make sense to add defaultDomain to all extractors? Originally the idea was to extract Catalogue of messages and just change domain from messages to specific domain, but then if some translations would be explicitly messages it would not work correctly.

I can add unit and functional tests right after when you confirm that something like this make sense.