Initial updates required to run under django 2.2

- Change to middleware.py
- Change some URLs formatting
- Fix django version at 2.2

InvenTree/build/migrations/0002_auto_20190412_2030.py

@@ -0,0 +1,25 @@
+# Generated by Django 2.2 on 2019-04-12 10:30
+
+import django.core.validators
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('build', '0001_initial'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='build',
+            name='part',
+            field=models.ForeignKey(limit_choices_to={'buildable': True}, on_delete=django.db.models.deletion.CASCADE, related_name='builds', to='part.Part'),
+        ),
+        migrations.AlterField(
+            model_name='build',
+            name='status',
+            field=models.PositiveIntegerField(choices=[(10, 'Pending'), (20, 'Holding'), (30, 'Cancelled'), (40, 'Complete')], default=10, validators=[django.core.validators.MinValueValidator(0)]),
+        ),
+    ]