implement LabelAssistant module

helps to  display proper labels for fields in forms
Multi step form for creating posters now works!

Few changes been made to PosterCleaner in order to distinguish
functionality for editing and and creating posters. NEEDS TO BE
REFACTORES CUZ UGLY!
clicking ’back’ on the form doesnt require fields to pass validation,
done with js.
special form just for editing posters
minor fix in posters index view