* Replace HEROKU_SLUG_COMMIT with custom footprint (naive)
* Fully set RELEASE_FOOTPRINT with the expectation of setting it before launch
* Change tests
* Fix cache
* Initial work for streaming app shell way of using serviceworkers
* Close in on serviceworker adjustment finalization
* Add docs and loading indicator
* Remove useless code
* Don't run on API
* Update app/javascript/contentDisplayPolicy/hideBlockedContent.js
* Fix small details
* Don't run serviceworker.js code in test env
* Fix JS in serviceworker
* Move private keyword to proper place in async controller
* Change shell_version to HEROKU_SLUG_COMMIT
* Update caching config
* Add test for async_info/shell_version
