More code modernization and moved the shared files to a shared location (for iOS and macos).
Modernized and improved the model by:
1) Moving the ivars out of the headers
2) Implementing properties, replacing getters and setters
3) Consistently naming ivars with _name, remaining consistent with property naming
4) Using forward declarations more aggressively
5) inits now return instanceType instead of id
6) Created FJVAvatar protocol for use in the model
Removed braces for ivars in public interface.  Adopted new literal array creation syntax.  Fixed a few variable names.