Improve RelatedField and callable default handling

- callable default values will now be properly called 
  - PrimaryKeyRelatedField and SlugRelatedField will now return an appropriate type based on the relation model's Field
  - mock views now have a request object bound even when public is True

testproj/articles/migrations/0001_initial.py

@@ -1,6 +1,8 @@
-# Generated by Django 2.0 on 2017-12-05 04:05
+# Generated by Django 2.0 on 2017-12-23 09:07
 
+from django.conf import settings
 from django.db import migrations, models
+import django.db.models.deletion
 
 
 class Migration(migrations.Migration):
@@ -8,6 +10,7 @@ class Migration(migrations.Migration):
     initial = True
 
     dependencies = [
+        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
     ]
 
     operations = [
@@ -15,12 +18,13 @@ class Migration(migrations.Migration):
             name='Article',
             fields=[
                 ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
-                ('title', models.CharField(help_text='Main article headline', max_length=255, unique=True)),
-                ('body', models.TextField(help_text='Article content', max_length=5000)),
-                ('slug', models.SlugField(blank=True, help_text='Unique URL slug identifying the article', unique=True)),
+                ('title', models.CharField(help_text='title model help_text', max_length=255, unique=True)),
+                ('body', models.TextField(help_text='article model help_text', max_length=5000)),
+                ('slug', models.SlugField(blank=True, help_text='slug model help_text', unique=True)),
                 ('date_created', models.DateTimeField(auto_now_add=True)),
                 ('date_modified', models.DateTimeField(auto_now=True)),
                 ('cover', models.ImageField(blank=True, upload_to='article/original/')),
+                ('author', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='articles', to=settings.AUTH_USER_MODEL)),
             ],
         ),
     ]

testproj/articles/migrations/0002_auto_20171221_1635.py

@@ -1,28 +0,0 @@
-# Generated by Django 2.0 on 2017-12-21 15:35
-
-from django.db import migrations, models
-
-
-class Migration(migrations.Migration):
-
-    dependencies = [
-        ('articles', '0001_initial'),
-    ]
-
-    operations = [
-        migrations.AlterField(
-            model_name='article',
-            name='body',
-            field=models.TextField(help_text='article model help_text', max_length=5000),
-        ),
-        migrations.AlterField(
-            model_name='article',
-            name='slug',
-            field=models.SlugField(blank=True, help_text='slug model help_text', unique=True),
-        ),
-        migrations.AlterField(
-            model_name='article',
-            name='title',
-            field=models.CharField(help_text='title model help_text', max_length=255, unique=True),
-        ),
-    ]