Replace all previously text-based json fields with JSONBlob

This JSONBlob field type is a wrapper around Django's new generic
JSONField, but with the database column type forced to be text.  This
should behave close enough to our old wrapper around
django-jsonfield's JSONField and will avoid needing to do the
out-of-band database migration.

awx/conf/migrations/0001_initial.py

@@ -4,6 +4,8 @@ from __future__ import unicode_literals
 from django.db import migrations, models
 from django.conf import settings
 
+import awx.main.fields
+
 
 class Migration(migrations.Migration):
 
@@ -17,7 +19,7 @@ class Migration(migrations.Migration):
                 ('created', models.DateTimeField(default=None, editable=False)),
                 ('modified', models.DateTimeField(default=None, editable=False)),
                 ('key', models.CharField(max_length=255)),
-                ('value', models.JSONField(null=True)),
+                ('value', awx.main.fields.JSONBlob(null=True)),
                 (
                     'user',
                     models.ForeignKey(related_name='settings', default=None, editable=False, to=settings.AUTH_USER_MODEL, on_delete=models.CASCADE, null=True),

awx/conf/migrations/0003_v310_JSONField_changes.py

@@ -1,11 +1,13 @@
 # -*- coding: utf-8 -*-
 from __future__ import unicode_literals
 
-from django.db import migrations, models
+from django.db import migrations
+
+import awx.main.fields
 
 
 class Migration(migrations.Migration):
 
     dependencies = [('conf', '0002_v310_copy_tower_settings')]
 
-    operations = [migrations.AlterField(model_name='setting', name='value', field=models.JSONField(null=True))]
+    operations = [migrations.AlterField(model_name='setting', name='value', field=awx.main.fields.JSONBlob(null=True))]