Implement a ALLOW_CERT_DELETION option (boolean, default False). When enabled, the certificate delete API call will work and the UI

will no longer display deleted certificates. When disabled (the default), the delete API call will not work (405 method not allowed)
 and the UI will show all certificates, regardless of the 'deleted' flag.

lemur/migrations/versions/318b66568358_.py

@@ -0,0 +1,23 @@
+""" Set 'deleted' flag from null to false on all certificates once
+
+Revision ID: 318b66568358
+Revises: 9f79024fe67b
+Create Date: 2019-02-05 15:42:25.477587
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = '318b66568358'
+down_revision = '9f79024fe67b'
+
+from alembic import op
+
+
+def upgrade():
+    connection = op.get_bind()
+    # Delete duplicate entries
+    connection.execute('UPDATE certificates SET deleted = false WHERE deleted IS NULL')
+
+
+def downgrade():
+    pass