Jacobi solver for PBD

• Fix ReducedFEM
• Fix some warnings in PbdModel
• Add Jacobi solver
  • Add Jacobi to non-collision solver
  • Add Jacobi to collision solver
• a bug that I just found: if PbdModel is initialized with Jacobi but switched to GS later, constraints will not be partitioned.
• Fix a bug in PBDModel::partitionConstraints that caused partitionedConstraints to be empty.
• Fix on a memory issue that causes large meshes to crush; It turned out the Welsh Powell coloring is the main cause of the issue.
• Add a new case, PBDSpeed, for PBD performance testing.
• It's better to have a test for coloring.
• Andrew's suggestion: separate GS and Jacobi into 2 classes
• Format the code