[WiP] User Checkin Manager

Added a page that allows us to check user's into the meeting. This allows us to quickly check a user in if he has trouble checking in using a meetup app.

It basically shows a page with alphabetic order users, a simple click on the user checks them in.

It still needs some styling if anyone wants to add or contribute please add to the PR, right now it looks decent. 

I'll review it tomorrow to see if i left anything out, just putting it up for more eyeballs to see it.