Allow users to choose which timers are saved

[ForeverWinter]

Instead of the "saved timers" list being auto-populated, let users choose which timers are saved by right click --> Add this timer to saved timers

Alternatively, create a new category of saved timers called "favorites" and options of "add to favorites" and "open favorite timers on startup"

[dziemborowicz]

Closing as a duplicate of #214.