Optimizations 1

- Maintain list of indices instead of particles in recursive lower bound
  method
- Scan the list only once for both weight-sum and mode instead of making 2
  scans
- Remove ObsNodeCollection
- Use "MAP" instead of unordered_map in Solver, with MAP defined to be std::map
  and changeable easily back to unordered_map
- Add a 11x11 rocksample configuration
- Change RockSample Model