Read EP data json files from disk

[octopusinvitro]

As we did in #58, it may be a good idea to read the popolo and countries files from disk, so that we don't get the 504 gateway time-out error when rawgit is down.

To keep these files up to date, we could add some lines to the deploy script so that it fetches the files just before deploying, and if there is an error it uses the files in the disk.