add created_by to notifications

this is so one-off notifications can be tied to a user
(jobs have a created_by, and api notifications don't make sense
 to have one)

migrations/versions/0100_notification_created_by.py

@@ -0,0 +1,27 @@
+"""add created_by col to notification
+
+Revision ID: 0100_notification_created_by
+Revises: 0099_tfl_dar
+Create Date: 2017-06-13 10:53:25.032202
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = '0100_notification_created_by'
+down_revision = '0099_tfl_dar'
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+def upgrade():
+    op.add_column('notifications', sa.Column('created_by_id', postgresql.UUID(as_uuid=True), nullable=True))
+    op.create_foreign_key(None, 'notifications', 'users', ['created_by_id'], ['id'])
+
+    op.add_column('notification_history', sa.Column('created_by_id', postgresql.UUID(as_uuid=True), nullable=True))
+    op.create_foreign_key(None, 'notification_history', 'users', ['created_by_id'], ['id'])
+
+
+def downgrade():
+    op.drop_column('notifications', 'created_by_id')
+    op.drop_column('notification_history', 'created_by_id')