User online status caching (#94)
* WIP on cron + Redis caching of connected users per locale
* Language support tweaks
* WIP on more logical locale support; fav users filtered by locale
* WIP on Redis caching of presence using sets; moved type definitions
* WIP on Redis caching of user presence data
* WIP on online user caching
* WIP but code is now consistent; needs test
* Cleanup of unused variables in firebase.py
* Added user parameter to render_template() calls; code formatting in cache.py
* Bug fixes in Redis online status handling code
* Added online user update job to cron.yaml
* Added TTL caching of online users
* Add attribution & copyright for Norwegian word frequency data
* Reduced in-memory caching of online users to 30 seconds
* Skip user online query if robots only
* Removed unused class
