Admins can now view list of admins - Fixes #38

[bhavyanshu]

Description

• Added feature that enables admins to view list of admins.
• Implemented in a controller in the Admin namespace and inherit from AdminController.
• Added link to view admins list in the appbar.

Fixes #38

Developer Checklist

• [x] I have read and followed the contribution guidelines.
• [x] All specs and linters pass (including Code Climate)
• [x] I have followed the style of nearby code
• [x] The build on Semaphore is successful
• [x] I have added tests for my changes and these tests would fail without my changes.
• [x] I have gone through my changes by hand, either in the browser or terminal, which ever makes sense
• [x] I have internationalized my changes

Maintainer Checklist

• [ ] Run migrations (if necessary) in production after deployment
• [ ] Review issues and update labels

[bhavyanshu]

@crawfoal I don't know if you got notified of my comment I posed up there. I think we should discuss where to put all the future admin action links before I make updates. Thanks!

[bhavyanshu]

@crawfoal I made the changes based on your suggestions. Let me know if there is anything else.

[crawfoal]

I went in and made one small correction to the translations keys that were used on the admin index page. Other than that, things look good, so I've merged your changes :)

Thanks for your contribution!