Ability to edit split length and re-arrange after mesocycle has started

[WhyAsh5114]

Is your feature request related to a problem? Please describe.

Currently the app locks mesocycle splits after a workout is added to the mesocycle, it is possible to remove that restriction.

Describe the solution you'd like

To achieve that, need to do the following:

• Avoid using total workouts as a calculation workoutsOfMesocycle.length
• Intelligently figure out splitDay changes, and apply them to all the WorkoutOfMesocycle relations by chaning their splitDayIndex