Use Que for background jobs instead Sidekiq

[beydogan]

Que uses PostgreSQL as background while Sidekiq is using Redis. Switching to Que will remove Redis dependency.

https://github.com/chanks/que
https://github.com/chanks/que/blob/master/docs/using_plain_connections.md

[simonoff]

@beydogan but will required a postgresql :)

[simonoff]

For such app better to use a sqlite. Its not so big.