Use `ActiveJob` for backgrounding contact

This will be `inline` and processed synchronously until the backend is
configured.
Removes redundant sidekiq job for contact mailer

Superseded by ActiveJob
Use `ActiveJob` for backgrounding identification

This will be `inline` and processed synchronously until the backend
is configured.
Removes redundant sidekiq job for identification

Superseded by ActiveJob
Removes now redundant sidekiq testing config
Merge pull request #42 from moneyadviceservice/inline-active-jobs

Replace Sidekiq mailing workers with ActiveJob