Translate model fields using ugettext_lazy rather than _l

Aliasing ugettext_lazy to _l does not work for translations as per this stackoverflow question:
http://stackoverflow.com/questions/16509160/ugettext-and-ugettext-lazy-functions-not-recognized-by-makemessages-in-python-dj

Reverted _l to the more verbose ugettext_lazy and removed the unnecessary intermediate solution of using translations.py file.