make chebR, chebXc properties of Polytope, Region
make chebR, chebXc properties of Polytope, Region

- auto-computed on first access
- protected from being set outside polytope module
- no need to import cheby_ball in addition to Polytope

necozay/tulip-control,tulip-control/tulip-control,necozay/tulip-control,tulip-control/tulip-control,tulip-control/tulip-control,necozay/tulip-control,necozay/tulip-control,necozay/tulip-control,tulip-control/tulip-control