Added foundation for conference 404/500 page - needs designs

[AndrewBestbier]

Gif

Motivation

Trello Ticket

React.London needs a 404 and 500 page. The designs for these pages are as follows:

500 Mobile 500 Tablet 404 Mobile 404 Tablet

Testing this ticket

Run React.London locally and access the following urls:

http://meetup-dev.react.london:8080/xx
http://dev.react.london:8080/xx

You should see the 404 pages for the meetup and conference pages respectively.

Then turn off your WIFI and access the same pages. This is simulating React London being unable to access Badger Brain. You should see the 500 pages for the meetup and conference pages respectively.

Code walkthrough

• I removed the unused Layout component. Not sure what the previous intended use for this was.
• I added CommunityLayout which is similar in structure to ConferenceLayout. It now contains the Header/Footer and has space for any child route.
• I adjusted our client side conference and community routes to show the 404 page if the * route is accessed. This route is the route called when no other route is found
• I adjusted the server side routes to show the respective 500 pages if there is a server error

[asavin]

Surely you only need retina 404_missing react_x2.png and you can remove the non-retina one

[asavin]

General comment - we could also serve 500 error page with a service worker for Chrome / FF browsers.

[zoeabryant]

I'm happy with this 👍 just change the svg thing!