Change the part preview UI element from QOpenGLWidget to QLabel, the preview images will be generated in an offscreen render.
This fixes the create multiple QOpenGLWidgets poor performace issue.
If one part configured color solubility, the generated color texture seam between the neighbor parts will be gradient filled using this part's color with the specified solubility.
Demo: https://twitter.com/jeremyhu2016/status/1132159910815227904
Currently, only support "Normal" and "Inversion" modes, "Normal" means normal mesh union, "Inversion" means mesh diff, it behaves like subtract itself from the previous mesh.
Many source file name and data type are prefixed by "skeleton" before, now all are refactored.
The class MeshResultContext represents the outcome of mesh generation before, now we have material, pose and animation, so we just rename it as Outcome.
huxingyi