Handle stale remote caches

[susannasiebert]

Currently, if the remote cache is stale (e.g. if there are issues with sidekiq in civic), users will encounter an infinite loop when calling civic.load_cache() (see #141). We should either fail, use the stale one, or automatically create an updated local cache. On failure we can instruct users to manually update their local cache using civicpy update --hard.