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/0013_auto_20200218_1639.py

@@ -0,0 +1,29 @@
+# Generated by Django 2.0.13 on 2020-02-18 16:39
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('assets', '0012_auto_20200218_1627'),
+    ]
+
+    operations = [
+        migrations.RemoveField(
+            model_name='asset',
+            name='circuits',
+        ),
+        migrations.RemoveField(
+            model_name='asset',
+            name='cores',
+        ),
+        migrations.RemoveField(
+            model_name='asset',
+            name='plug',
+        ),
+        migrations.RemoveField(
+            model_name='asset',
+            name='socket',
+        ),
+    ]