form key ordering: detect django version
form key ordering: detect django version

- Django 1.6 and before use SortedDict instead of OrderedDict
  It detect version and return proper dict for key ordering.
- field deletion is done by reorder funcion.

Signed-off-by: Hiroshi Miura <ff6fb3ed059786151e736af13627c08d24e9f922@linux.com>

faulteh/symposion,pydata/symposion,miurahr/symposion,pinax/symposion,pydata/symposion,pyconau2017/symposion,pinax/symposion,faulteh/symposion,miurahr/symposion,pyconau2017/symposion,pyohio/symposion,pyohio/symposion