Add OPG to letter organisations

Logo was added here:
https://github.com/alphagov/notifications-template-preview/pull/19

migrations/versions/0105_opg_letter_org.py

@@ -0,0 +1,28 @@
+"""empty message
+
+Revision ID: 0105_opg_letter_org
+Revises: 0104_more_letter_orgs
+Create Date: 2017-06-29 12:44:16.815039
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = '0105_opg_letter_org'
+down_revision = '0104_more_letter_orgs'
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+from flask import current_app
+
+
+def upgrade():
+    op.execute("""
+        INSERT INTO dvla_organisation VALUES
+        ('002', 'Office of the Public Guardian')
+    """)
+
+
+def downgrade():
+    # data migration, no downloads
+    pass