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

This replaces the hardcoding of colours in the asset list.

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.'),
+        ),
+    ]