Group specific fields in horizon.form module

    According to the Django architecture, all fields are grouped in
the django.form module, Horizon fields were dispatched in two modules
utils and form. This patch cleanup the loading of Horizon specific
fields.

Change-Id: Ib18848a8cc06dbd5984ec02d7cd647145124ced4
Closes-Bug: #1287634
Merge "Group specific fields in horizon.form module"