Fine-tuning DB model and create taks for data migration

- Removed unused columns in ft_billing
- Create tasks for nightly data migration

migrations/versions/0178_billing_primary_const.py

@@ -0,0 +1,36 @@
+"""
+
+Revision ID: 24f47fae3660
+Revises: 0178_billing_primary_const
+Create Date: 2018-03-13 14:52:40.413474
+
+"""
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+revision = '0178_billing_primary_const'
+down_revision = '0177_add_virus_scan_statuses'
+
+
+def upgrade():
+    op.drop_column('ft_billing', 'crown')
+    op.drop_column('ft_billing', 'annual_billing_id')
+    op.drop_column('ft_billing', 'organisation_id')
+    op.drop_constraint('ft_billing_pkey', 'ft_billing', type_='primary')
+    # These are the orthogonal dimensions that define a row (except international).
+    # These entries define a unique record.
+    op.create_primary_key('ft_billing_pkey', 'ft_billing', ['bst_date',
+                                                            'template_id',
+                                                            'rate_multiplier',
+                                                            'provider',
+                                                            'international'])
+
+
+def downgrade():
+    op.add_column('ft_billing', sa.Column('organisation_id', postgresql.UUID(), autoincrement=False, nullable=True))
+    op.add_column('ft_billing', sa.Column('annual_billing_id', postgresql.UUID(), autoincrement=False, nullable=True))
+    op.add_column('ft_billing', sa.Column('crown', sa.TEXT(), autoincrement=False, nullable=True))
+    op.drop_constraint('ft_billing_pkey', 'ft_billing', type_='primary')
+    op.create_primary_key('ft_billing_pkey', 'ft_billing', ['bst_date',
+                                                            'template_id'])