This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
* set up static offline.html route and service worker for Android Web App Banner
* add viewport meta tag to offline view for android app banner
* add i18n support for offline.html pages, cleanup
* fix html syntax, add page title, remove license for service-worker.js