Track time-played per game

[hrydgard]

Commonly requested feature and fairly easy to implement, so here it is, at least the basics.

Tracking is done per game-id, and fast-forward/slowdown is currently ignored (so times won't be comparable for the purposes of speed running, I suppose).

Left to do before merging:

• Correct tracking during pause
• Redesign game info screen to fit the new text
• Update translation strings. Maybe include days, too, in addition to hours:minutes:seconds?
• Maybe show time played on pause screen too?

Out-of-scope:

• Correctly handling time tracking when paused in the debugger

Fixes #18410