feat: body parts to include front and back separation as well

[zoltan-varga]

Description

Currently, there is only a right and left separation, and, for example, the tummy and the lower back is selected at the same time. This must be separated. Massage therapist usually don't care about right or left, but they care about front and back.

For a much comprehensive improvement, the body parts should be totally dynamic instead of a fixed set. Somebody needs more detail and the other one needs less detailed separation of the body parts.

Requirements

• Body parts to be defined flexibly when instantiating the object.
• by default, back and front body parts should be separated

Additional Context

Add any other context or screenshots about the feature request go here.