more best practices fixes

- Adds more `const` in getters
- Overriden methods have the `override` keyword
- Reorganizes the structure of the class:
  # creators first, then constructor, destructors, init
  # then overridden methods
  # variables at the end
- removes Hungarian notation from parts of the code
Merge branch 'more_best_practices_fixes' of https://github.com/ricardoquesada/cocos2d-x into ricardoquesada-more_best_practices_fixes

Conflicts:
	cocos2dx/actions/CCActionTiledGrid.h
Merge pull request #3187 from dumganhar/ricardoquesada-more_best_practices_fixes

Merge https://github.com/cocos2d/cocos2d-x/pull/3183