Add offline capabilities using offix-client

[darahayes]

npm.im/offix-client can be used almost as a drop in replacement for apollo client.

There are a couple of minor things that need to be done to get it into the app properly.

I just started working on a very basic React app that uses offix-client which has some patterns for integrating and using the offix client.

https://github.com/darahayes/offix-example-react

There are a couple of key things to be aware of.

• You can copy this file which initializes the offix client. You might need to change the server urls and any other config we already have for the current set up. You can also comment out/remove the mutationCacheUpdates bit for now.
• You will need to wrap the app with an <OffixProvider> component. This is similar to what is probably being done already with ApolloProvider. You can see that being done here: https://github.com/darahayes/offix-example-react/blob/master/src/index.tsx#L9-L16
• Within the App Component itself, you will still use the ApolloProvider component, but there is some extra code needed to get things to work. Instead of requiring and creating an Apollo Client the normal way, you will get the Apollo Client that comes from the offix client. You can see that being done here: https://github.com/darahayes/offix-example-react/blob/master/src/components/App.tsx#L31-L56

Once that's done, the client app should work as it has before with no noticeable difference. Ping @milenazuccarelli