Adding queryFilter possibility to objects.

[lombao]

In the managed,json I can use the hooks onCreate onUpdate and so to implement some access controls based on the atributes of the user that requests it, but I can limit what the requester sees with a query , it woud be nice to have something that validates each object returned on a query, something similar to the validTarget or validSource in a mapping.

[lombao]

Just realized this can be implemented with a custom endpoint, and forcing the use of this custom endpoint instead of the "standard" /managed/user resource.

[vharseko]

Please check #139