Feature: Prevent me from accidentally deleting a workout

[pepopowitz]

In #33, I added the ability to delete a workout from the edit modal.

Unfortunately, it's pretty easy to click the button and accidentally delete something.

Since it's in a modal already, popping a confirmation modal seems not great. Instead I want to make a fancy delete button that requires two clicks within a certain amount of time. If you wait too long, it will return to a state where it requires two clicks.