Added a new rates table.

We only need one rate per channel. This reflects that. The provider_rates has been left for now, it is still not being used.
New dao has been added to select the right rate for the given notification_type and date of notificaiton.

migrations/versions/0075_create_rates_table.py

@@ -0,0 +1,40 @@
+"""empty message
+
+Revision ID: 0075_create_rates_table
+Revises: 0074_update_sms_rate
+Create Date: 2017-04-24 15:12:18.907629
+
+"""
+
+# revision identifiers, used by Alembic.
+import uuid
+
+revision = '0075_create_rates_table'
+down_revision = '0074_update_sms_rate'
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+def upgrade():
+    notification_types = postgresql.ENUM('email', 'sms', 'letter', name='notification_type', create_type=False)
+    op.create_table('rates',
+    sa.Column('id', postgresql.UUID(as_uuid=True), nullable=False),
+    sa.Column('valid_from', sa.DateTime(), nullable=False),
+    sa.Column('rate', sa.Numeric(), nullable=False),
+    sa.Column('notification_type', notification_types, nullable=False),
+    sa.PrimaryKeyConstraint('id')
+    )
+
+    op.create_index(op.f('ix_rates_notification_type'), 'rates', ['notification_type'], unique=False)
+
+    op.get_bind()
+    op.execute("INSERT INTO rates(id, valid_from, rate, notification_type) "
+               "VALUES('{}', '2016-05-18 00:00:00', 1.65, 'sms')".format(uuid.uuid4()))
+    op.execute("INSERT INTO rates(id, valid_from, rate, notification_type) "
+               "VALUES('{}', '2017-04-01 00:00:00', 1.58, 'sms')".format(uuid.uuid4()))
+
+
+def downgrade():
+    op.drop_index(op.f('ix_rates_notification_type'), table_name='rates')
+    op.drop_table('rates')