feat: Muscle group specific functionality

[Mafeffe]

It would be useful to have some way of tracking how much exercise each muscle group is getting. This would make it easier to see which muscle groups are getting overworked and which groups are getting underworked (NEVER SKIP LEG DAY).

This could be done by adding "Worked muscles" to each of the saved exercises, where one could select which muscles are worked. Some exercises mainly work specific muscles, but use other muscles as support. In the fitness community it is common to count each set of exercise as half a set for a supporting muscle group. An example would be row exercises. Let's say we do 4 sets of barbell rows. The back muscles (lats) would then get 4 sets added to the sum of exercise, but the supporting muscles (biceps) would only get 2 sets added (0.5 weighting).

The muscle groups that are able to be selected need to be considered. The back should probably be divided into 3 or 4 different groups (lats, center, upper, lower). Legs at least 3 groups (quad, hamstring, calf). 4 groups if glutes counts as legs.