Added implementation of TradingStage

* Implemented has only been through preliminary tests
Game now consists of one instance of TradingStage for testing purposes
Merge branch 'development' into trading_stage

* need minor fixes
Cleaned up code, implemented new functions

update_player_info, item activation, UI updates, removal of vestigal
code, implemented new tests
UI updates
Improved trading UI logic
Finished trade_proposed and added player inventory and health status

* also changed log messages to include player number
Merged and fixed minor bug in trade_proposed and player inventory handling
Minor updates
Merge branch 'trading_stage' of https://github.com/iteloo/the_island into trading_stage

Conflicts:
	assets/main.js
Merge branch 'trading_stage' into development