Fix widget getting hidden
Fix widget getting hidden

Since the commit in django below, widgets with input_type hidden are hidden entirely.
Override is_hidden to prevent this from happening.

Affects Django version v1.7 and up.

https://github.com/django/django/commit/dc3d2ac98c1bcfad74d3e9523caf07e7e9fb15aa
bennylope/django-taggit-labels,bennylope/django-taggit-labels