merge latest changes from ReForm
- Implement the MISolver stack with Eigen instead of GMM.
- Make GMM an optional dependency. (CoMISo has only one remaining required dependency for using the constrained mixed integer solver, Eigen3.)
- Two new solvers
- Solver/MultiDimConstrainedSolver as a wrapper around ConstrainedSolver to simplify solving problems with multiple independent dimensions.
- Solver/SubProblemSolver as a wrapper around MultiDimConstrainedSolver which automatically remaps all used indices to the range 0..n suitable for solving.