Adds field on import job to check if job completed

the task isn't a reliable indicator, unfortunately.

bookwyrm/migrations/0034_importjob_complete.py

@@ -0,0 +1,18 @@
+# Generated by Django 3.0.7 on 2021-01-07 16:07
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('bookwyrm', '0033_siteinvite_created_date'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='importjob',
+            name='complete',
+            field=models.BooleanField(default=False),
+        ),
+    ]