Allow server to decide to make a timer by ID visible or not

[Chrezm]

Something like this

TV#<timer_id: int>#<visible: int (0 or 1)>

TV#0#0 : Hides timer 0 (if timer 0 exists)
TV#3#1 : Shows timer 3 (f timer 3 exists)

Edge cases:

• If timer_id is a negative number or not a number less than the number of timers the theme has allocated, this function does nothing.
• If timer_id is already hidden and the command mandates to hide the timer, this function does nothing. Similar behavior if the timer is shown and the command mandates to show the timer.
• Hiding or showing a timer should have no effect on whether the timer is paused or not, the firing interval, or step length.