Sync user repos async

[gomayonqui]

• Sync users and repos with sidekiq workers every sunday midnight.
• Add sidekiq dashboard only for admin users (added a migration for admin attribute).
• Add whenever to schedule tasks

[orendon]

What an awesome feature @gomayonqui :+1:

Btw, would be nice to add repos synchronization to sidekiq queue too. See users_controller.rb

Currently repos sync occurs during user sign in/sign up which slow down the whole request, we can move that to the queue or even better adding a "Synchronize Repos" button so the user can sync manually.

[orendon]

@gomayonqui did you figured out the sidekiq start/restart issue locally? Vagrant image provided would be ideal for that