Detect type of SlugRelatedField with readonly=True (#83)

* Added test for #82 - readonly SlugRelatedField not showing format uuid
* Added ArticleGroup model
* Added example of SlugRelatedField to a uuid field with and without readonly
* Check remote_field.model in get_related_model

Closes #82.

testproj/articles/migrations/0003_auto_20180310_0142.py

@@ -0,0 +1,36 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.11 on 2018-03-10 01:42
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+import django.db.models.deletion
+import uuid
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('articles', '0002_article_article_type'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='ArticleGroup',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('uuid', models.UUIDField(default=uuid.uuid4, editable=False, unique=True)),
+                ('title', models.CharField(help_text='title model help_text', max_length=255, unique=True)),
+                ('slug', models.SlugField(blank=True, help_text='slug model help_text', unique=True)),
+            ],
+        ),
+        migrations.AddField(
+            model_name='article',
+            name='group',
+            field=models.ForeignKey(blank=True, default=None, on_delete=django.db.models.deletion.PROTECT, related_name='articles_as_main', to='articles.ArticleGroup'),
+        ),
+        migrations.AddField(
+            model_name='article',
+            name='original_group',
+            field=models.ForeignKey(blank=True, default=None, on_delete=django.db.models.deletion.PROTECT, related_name='articles_as_original', to='articles.ArticleGroup'),
+        ),
+    ]