Fixes #3266 - Cell timers will no longer start automagically

* Cell timers will no longer start counting down automagically
* Made cell timers use world.timeofday instead of world.time
* Separated the countdown timer and the "set timer" controls
* You can now modify the cell timer without fucking up the countdown entirely
* Absolute paths, because
Committing changelog
Merge pull request #3362 from Kilakk/dev

Fixes #3266 - Cell timers will no longer start automagically