Implement item update and deletion.

Deletion is essentially an update with "isDeletion" set to True.

django_etesync/migrations/0013_collectionitemrevision_is_deletion.py

@@ -0,0 +1,18 @@
+# Generated by Django 3.0.3 on 2020-02-26 13:17
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('django_etesync', '0012_auto_20200220_2038'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='collectionitemrevision',
+            name='is_deletion',
+            field=models.BooleanField(default=False),
+        ),
+    ]

django_etesync/migrations/0014_auto_20200226_1322.py

@@ -0,0 +1,18 @@
+# Generated by Django 3.0.3 on 2020-02-26 13:22
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('django_etesync', '0013_collectionitemrevision_is_deletion'),
+    ]
+
+    operations = [
+        migrations.RenameField(
+            model_name='collectionitemrevision',
+            old_name='is_deletion',
+            new_name='isDeletion',
+        ),
+    ]

django_etesync/migrations/0015_auto_20200226_1349.py

@@ -0,0 +1,18 @@
+# Generated by Django 3.0.3 on 2020-02-26 13:49
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('django_etesync', '0014_auto_20200226_1322'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='collectionitemrevision',
+            name='current',
+            field=models.BooleanField(blank=True, db_index=True, default=True, null=True),
+        ),
+    ]