Rename 'Progress' button to 'Save' or 'Confirm' when logging an exercise

When logging an exercise, there is a button named 'Progress'. This name gives the impression that the set must be better than last time, while in practice the button simply saves the set, even if fewer reps were done than before. A clearer name such as 'Save' or 'Confirm' better matches the button's actual function and prevents confusion for members.