Miscellaneous changes to the Asset DB (#390)

* FIX #388: Prevent assets losing supplier data on edit

* FEAT: Add associated assets to supplier detail view

* FIX: Tweak supplier list to make detail view accessible

* Potential fix for #380

No idea if it works because I can't reproduce locally. S/O Reckons it should... :P

* FEAT #386: Asset search searches serial number.

Pending addition of advanced search.

* FIX: Order asset categories/statuses alphabetically

Instead of by pk because that's silly.

* FEAT: Statuses can have a CSS class defined in the admin panel

This replaces the hardcoding of colours in the asset list.

* FIX: Squash migrations

* Fixed supplier not working on all the create asset template

* Refactored away "assets" property on "Supplier" by using "related_name" instead

Co-authored-by: Matthew Smith <mattysmith22@googlemail.com>

assets/migrations/0010_assetstatus_display_class.py

@@ -0,0 +1,18 @@
+# Generated by Django 2.0.13 on 2020-01-02 19:35
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('assets', '0009_auto_20200102_1933'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='assetstatus',
+            name='display_class',
+            field=models.TextField(default='', help_text='HTML class to be appended to alter display of assets with this status, such as in the list.'),
+        ),
+    ]