Add deconstruct methods to fields with custom keywords

Fields that are adding keyword arguments to custom fields require a ``deconstruct`` method to make the keywords available in the corresponding migration(s). The [Django 1.7 documentation provides more details](https://docs.djangoproject.com/en/dev/howto/custom-model-fields/#field-deconstruction).

Without the ``deconstruct`` method, the custom keywords are not added to the migrations and are therefore ignored when the migrations are run. In my case, the migrations failed because ``auto_add`` was not set during the migrations of the ``UUIDField``.

I have added ``deconstruct`` methods to th ``ArrayField``, ``JSONField`` and ``UUIDField`` adding the custom keywords accordingly. Please take a look and let me know if you are happy with that or have any suggestions to improving it.

Oh, and thanks for a great Django app :thumbsup:.