Function 'localize' moved to ServicesManagerTarget library

- bnc#886117
- added test case
- tested in latest build and the fix works
- tested with `rake osc:build` and passes

I'd use some more descriptive comments for translators, "Default target" does not tell much unless you are `systemd` expert, also "Graphical" itself is not much user friendly. Something like "Graphical Login" would be better IMHO. The same for "Multi-user"...

(But yes, we are after the text freeze, and this is not critical, so you can leave it as it is. It's just a minor issue...)