Jacobi/SOR of PBD
- Fix some warnings in PbdModel
- Add Jacobi solver
- Fix a bug in PBDModel::partitionConstraints that caused partitionedConstraints to be empty.
- Add PBDSpeed for PBD performance testing; add PBDJacobiVsGS to compare Jacobi and GS.
- Andrew's suggestion: separate GS and Jacobi into 2 classes.
- Move partitioning-related data from PbdModel into PbdSolver. This makes more logical sense since the partitioning is solver dependent.