Made $map protected and moved it to __construct()

By making $map protected and moving the actual declaration to the 
__construct, you make it easier to extend the BasicPermissionMap.

At the moment, if you want to extend it, you have to copy/paste the 
entire $map variable into your own class. I feel it makes more sense
to call the parent::__construct in your own mapping and add your own 
mappings to the variable, instead of having to replace it completely.