srmnitc/pyscal: Addition of Centrosymmetry parameter and common neighbor analysis

This release adds a number of new changes to the code: Major changes

• Remove pickling support
• Add variable conditions for clustering
• Add new neighbor method which finds N nearest neighbors
• Add centrosymmetry parameter with two algorithms
• Add Common Neighbor Analysis and adaptive CNA

Minor changes

• traj process:
  • poscar with selective dynamics can be read in
  • add write poscar method
  • split trajectory will automatically remove incomplete snapshots
• Add misc module which has methods to compare atomic environments
• system
  • remove stale indicator functions
  • restructure system code and clean up
• atom
  • remove access functions and implement read_write
  • restructure atom code and clean up
• faster chi params method
• documentation updates
• remove access functions and implement read write