Implement onSessionLogin trigger for commands.yml (#1198)

* Implement onSessionLogin trigger for commands.yml

Needs test methods, @ljacqu any advice?

* Add simple onSessionLogin test

src/main/resources/commands.yml

@@ -24,9 +24,10 @@
 #     command: 'broadcast %p has joined, welcome back!'
 #     executor: CONSOLE
 # 
-# Supported command events: onLogin, onJoin, onRegister, onUnregister
+# Supported command events: onLogin, onSessionLogin, onJoin, onRegister, onUnregister
 onJoin: {}
 onLogin: {}
+onSessionLogin: {}
 onRegister: {}
 # Commands to run whenever a player is unregistered (by himself, or by an admin)
-onUnregister: {}
+onUnregister: {}