Option to remove the generic aliases which MAY clash

This pull request solves https://github.com/mperham/sidekiq/issues/1647.

Please add `Sidekiq.namespace_delay_methods` to your config/initializers/sidekiq.rb and the DangerousAttributeErrors will go away.

Instead of the `delay`, `delay_for` and `delay_until` methods,
use
`sidekiq_delay`
`sidekiq_delay_for` and
`sidekiq_delay_until` respectively

Hope this helps