200 refactor volunteer registrationcheck in flow

[theNatePi]

Changes

• Matched design flow
• Event side bar now conditionally shows check in or cancel registration
  • For both mobile and desktop
• Only upcoming, non-registered events will show up on the events page
• Only past/upcoming registered events show up on the volunteer home page
• The events stats thing is also conditionally rendered
• Updated featured events to show two most recent upcoming non-registered events

Testing

• Made new user account
• Registered from events, unregistered
• Confirmed events only showed up on the right page and that the side bar was rendered correctly
• Confirmed event was deleted from event_data when user unregistered

Backend

• Created new backend route
• /data/unregistered/:volunteerid:
• See backend branch by same name

[Aokijiop]

Nice job guys!