Added OnPlayerChat for messages to 1 player only.

This is tested up to line 3439 of FrostbiteClient.cs (inside DispatchPlayerOnChatRequest). The if statement is true if a server message is sent to a specific player. I couldn't get the PlayerChat handler to not be null, as I couldn't get PluginManager.AssignEventHandlers() to run. However, if AssignEventHandlers() works, this should work. This needs to be tested though.