add watch toggle setting

[art0007i]

resolves #521

[galister]

This makes it so that you'd need to restart wayvr after toggling the checkbox.

It would make more sense to create the watch regardless of the setting. Simply hide by unsetting its active_state

[art0007i]

Well actually it deletes and recreates the watch dynamically when you toggle the checkbox but I can rework it to use the active state, since that seems like a cleaner approach anyway

[galister]

neat, thanks.

i think there's a discrepancy in this that if the user places the watch on their right hand then toggles the watch off and back on, it will be back on the left hand. but this is not really easy to solve right now so it's fine to look at it later

it would likely involve using OverlayTask::ToggleOverlay instead of activate/deactivate. the former reads/writes states while the activate/deactivate is more for throwaway overlays like toasts etc.

[galister]

do another cargo fmt and it's good then

[galister]

thanks!