Simple Player Trades

Added /trade command to send a trade request
Added /tradeaccept command to accept an incoming request
Added /tradedeny command to deny an incoming request
Added /tradecancel command to cancel an outgoing request or active trade
Added shared double chest trade GUI
Shift-click support for moving items in and out of the trade window
Both players must click the green accept button to confirm before the trade executes
Clicking the red cancel button closes the trade and returns all items
Moving items after confirming automatically resets your confirmation
The center divider turns green when a player confirms, with a sound notification
Trade requests automatically expire after a configurable timeout
Cooldown between trade requests
Trade logging to file with full item details
Log files rotate automatically
Config file at config/simple-player-trades/config.properties
Server admins can disable trading entirely via config
Server admins can restrict trading to opped players only via config