Implement partial coefficients setter for Face

[definability]

During fitting procedure Face can be modified partly. Part of #64

Need to change coefficients of Face and store indices of changed ones there until the model will be drawn

• partial setter for coefficients (use new Face instead of entire setter);
• getter for changed coefficients (or indices of changed ones).

Will diff be helpful to avoid storing coefficients values inside of View and just add them?

Deprecate logic of Face creation in MFM, because all calculations will happen in shaders and Face becomes just a storage for model parameters.