Option to keep the task list open when clicking Today

Clicking Today while you're already on Today opens or closes the task list next to the calendar. Some users almost always want the task list open, and an accidental double-click on Today closes it. Add an option so Today never closes the task list. The panel would then only be closed with the « button at the top of the calendar.

Original request from Elliot: "I almost always want to have that one panel open, and it's really frustrating that if I double-click the Today view accidentally, it'll close it."