Add a way to override hasPermission method

[LoisDuplain]

Permission manager plugins needs to override hasPermission method.

Can be used like any other events:

	public void handlePlayerCheckPermissionEvent(PlayerCheckPermissionEvent event) {
		boolean hasPermission = event.hasPermission();

		if (hasPermission)
			return;
		
		final Player player = event.getPlayer();

		// Your behavior

		event.setHasPermission(/* true or false */);
	}

[HSGamer]

I did something similar but for PermissionHandler #1138 Man, it's old now.

[dev-hydrogen]

@LoisDuplain you should probably address the issues i commented on if you still want this merged (though no guarantee it even will be, since no contributors have commented on this yet)