Add organisation_id to Service.

This is the second commit in the series to add organisation_id to Service.
- Data migration to update services.organisation_id from data in organisation_to_service
 (The rollback will lose any updates to organisation unless the script is updated to set organistion_to_service from service.organisation_id )
- Update Service.organisation relationship to a ForeignKey relationship to Organisation.
- Update Organisation.services to a backref relationship to Service.

migrations/versions/0303_populate_services_org_id.py

@@ -0,0 +1,30 @@
+"""
+
+Revision ID: 0303_populate_services_org_id
+Revises: 0302_add_org_id_to_services
+Create Date: 2019-08-06 09:43:57.993510
+
+"""
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+revision = '0303_populate_services_org_id'
+down_revision = '0302_add_org_id_to_services'
+
+
+def upgrade():
+    sql = """
+        UPDATE services
+           SET organisation_id = (SELECT organisation_id from organisation_to_service 
+                                  where organisation_to_service.service_id = services.id)
+    """
+    op.execute(sql)
+
+
+def downgrade():
+    sql = """
+        UPDATE services
+           SET organisation_id = null
+    """
+    op.execute(sql)