Move job queue to redis

We'll use it as cache in the future.

/!\ You'll loose your old jobs (pending jobs too) so upgrade only when
you don't have pending job anymore.

server/helpers/database-utils.ts

@@ -16,6 +16,7 @@ function retryTransactionWrapper <T> (
         .catch(err => callback(err))
   })
   .catch(err => {
+    console.error(err)
     logger.error(options.errorMessage, err)
     throw err
   })