Add view tests

• Introduce framework to simply test correct rendering of views
• Create tests for dashboard views
• Create tests for plan views
• Create tests for default admin views (add and change) of AKModel models
• Create tests for scheduling (admin) views
• Create tests for submission views
• Improve pipeline to correctly run the new tests on a blank database with fixture loading
• Add coverage reporting
• Show test results in GitLab directly

AKScheduling/tests.py

-# Create your tests here.
+from django.test import TestCase
+from AKModel.tests import BasicViewTests
+
+
+class ModelViewTests(BasicViewTests, TestCase):
+    fixtures = ['model.json']
+
+    VIEWS_STAFF_ONLY = [
+        ('admin:schedule', {'event_slug': 'kif42'}),
+        ('admin:slots_unscheduled', {'event_slug': 'kif42'}),
+        ('admin:constraint-violations', {'slug': 'kif42'}),
+        ('admin:special-attention', {'slug': 'kif42'}),
+        ('admin:cleanup-wish-slots', {'event_slug': 'kif42'}),
+        ('admin:autocreate-availabilities', {'event_slug': 'kif42'}),
+        ('admin:tracks_manage', {'event_slug': 'kif42'}),
+        ('admin:enter-interest', {'event_slug': 'kif42', 'pk': 1}),
+    ]