offline capabilities

[pkra]

It would be nice to enable Lens to load when offline. A serviceworker would be fancy but a manifest would probably take us most of the way. This would need some gulp work to automate.

[pkra]

I played around with appcache for the first time. It's simple enough but a little weird at times (cf http://alistapart.com/article/application-cache-is-a-douchebag). The only thing I couldn't yet make to work are the remote resources (cf also #8).

Will try serviceworkers for comparison.

[pkra]

ServiceWorker is also easy (since we just need a cache). If we fix #8, then appcache will work ok.

Since appcache is deprecated (in terms of spec) and FF & Chrome are planning to actually remove their support, we should implement both.