Add migration to migrate user_total view to use contributions
user
```ruby
class MigrateUserTotalViewToContributions < ActiveRecord::Migration
  def up
    execute <<-SQL
      DROP VIEW user_totals;
      CREATE OR REPLACE VIEW user_totals AS
      SELECT
        b.user_id as id,
        b.user_id,
        count(DISTINCT(b.project_id)) as total_contributed_projects,
        sum(b.value) AS sum,
        count(*) AS count,
        sum(CASE
          -- I've contributed a successful (or unfinished) project with money
          WHEN (p.state <> 'failed') AND NOT b.credits THEN 0

          -- I've contributed a failed project with credits
          WHEN p.state = 'failed' AND b.credits THEN 0

          -- I've contributed a failed project with money and asked for refund xor I've contributed a failed project with credits
          WHEN p.state = 'failed' AND ((b.state IN('requested_refund', 'refunded') AND NOT b.credits) OR (b.credits AND NOT b.state IN('requested_refund', 'refunded') )) THEN 0

          -- I've contributed a failed project with money and did not ask for refund
          WHEN p.state = 'failed' AND NOT b.credits AND b.state = 'confirmed' THEN b.value

          -- I've contributed a successful project with credits
          ELSE b.value * (-1)::numeric
        END) AS credits
      FROM
        contributions b
        JOIN projects p ON (b.project_id = p.id)
      WHERE b.state in ('confirmed', 'requested_refund', 'refunded')
      GROUP BY b.user_id;
    SQL

  end

  def down
    execute <<-SQL
      DROP VIEW user_totals;
      CREATE OR REPLACE VIEW user_totals AS
      SELECT
        b.user_id as id,
        b.user_id,
        count(DISTINCT(b.project_id)) as total_backed_projects,
        sum(b.value) AS sum,
        count(*) AS count,
        sum(CASE
          -- I've backed a successful (or unfinished) project with money
          WHEN (p.state <> 'failed') AND NOT b.credits THEN 0

          -- I've backed a failed project with credits
          WHEN p.state = 'failed' AND b.credits THEN 0

          -- I've backed a failed project with money and asked for refund xor I've backed a failed project with credits
          WHEN p.state = 'failed' AND ((b.state IN('requested_refund', 'refunded') AND NOT b.credits) OR (b.credits AND NOT b.state IN('requested_refund', 'refunded') )) THEN 0

          -- I've backed a failed project with money and did not ask for refund
          WHEN p.state = 'failed' AND NOT b.credits AND b.state = 'confirmed' THEN b.value

          -- I've backed a successful project with credits
          ELSE b.value * (-1)::numeric
        END) AS credits
      FROM
        backers b
        JOIN projects p ON (b.project_id = p.id)
      WHERE b.state in ('confirmed', 'requested_refund', 'refunded')
      GROUP BY b.user_id;
    SQL

  end
end
```
assistant