Visibility.js provides a thin wrapper over page visibility API, which
allows to detect if page is currently visible by user. This allows us to
stop live updates when it's not needed. This is especially easy in case
of timers, because Visibility.js provides setInterval replacement, which
runs given code only when page is visible.
A lot of ❤️ for @tchack, who showed me visibility.js!
It seems that running Ember.run.later periodically can cause CPU usage
to increase over time. Such increase adds up to already increasing CPU
usage because of data amount growing.
This commit tries to mitigate the issue by using setTimeout instead
