Use new IPFS gateway for GET fetches

When adding the gateway URL, the wrapper will do a normal fetch to
`https://ipfs.kosmos.org/ipfs/$hash` instead of using the generic POST
requests to the IPFS API endpoint. This enables normal browser caching
for all IPFS documents in this app.

config/environment.js

@@ -40,7 +40,8 @@ module.exports = function(environment) {
     ipfs: {
       host: 'ipfs.kosmos.org',
       port: '5444',
-      protocol: 'https'
+      protocol: 'https',
+      gatewayUrl: 'https://ipfs.kosmos.org/ipfs'
     }
   };