Allow configuration of permission granting strategy

The DefaultPermissionGrantingStrategy does not work correctly with CumulativePermission. It would be nice to allow users to override the aclPermissionGrantingStrategy in their application's context and for this strategy to be used when AclImpl objects are instantiated.
Inject permissionGrantingStrategy
Use injected permissionGrantingStrategy when instantiating AclImpl objects
Merge pull request #9 from tcrossland/patch-1

Allow configuration of permission granting strategy