- add ballance params section and successive switch in virtools file exporter to allow user manually cancel sector group ensurance which give user a way to export component, not the whole level.
- add mirror matrix detection in bme creation. a mirror matrix will reverse triangle indice order. we need reverse it again when facing mirror matrix. this resolves the issue when applying term 3.
- use mirror, not rotation to create straight floor in bme which give a better looks in game.
