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/0014_auto_20200218_1840.py

@@ -0,0 +1,17 @@
+# Generated by Django 2.0.13 on 2020-02-18 18:40
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('assets', '0013_auto_20200218_1639'),
+    ]
+
+    operations = [
+        migrations.AlterModelOptions(
+            name='cabletype',
+            options={'ordering': ['plug', 'socket', '-circuits']},
+        ),
+    ]