Add 'CableTypes' (#406)

* Move relevant fields and create migration to autogen cable types

* CRUD and ordering

* FIX: Prevent creating duplicate cable types

* FIX: pep8/remove debug print

* FIX: Meta migrations... :>

* FIX: Update tests to match new UX

* Move cabletype menu links into 'Assets' dropdown

* Fix migration

* Specify version of reportlab

Should fix CI - looks like I went a bit too ham-handed in my requirements.txt purge last time...

assets/migrations/0011_auto_20200218_1617.py

@@ -0,0 +1,29 @@
+# Generated by Django 2.0.13 on 2020-02-18 16:17
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('assets', '0010_auto_20200219_1444'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='CableType',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('circuits', models.IntegerField(blank=True, null=True)),
+                ('cores', models.IntegerField(blank=True, null=True)),
+                ('plug', models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='plug', to='assets.Connector')),
+                ('socket', models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='socket', to='assets.Connector')),
+            ],
+        ),
+        migrations.AddField(
+            model_name='asset',
+            name='cable_type',
+            field=models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, to='assets.CableType'),
+        ),
+    ]