WPS service child items to represent processes

[fmigneault]

Magpie services of type ServiceWPS for WPS-1/2 does not allow child resources.
This causes a problem because requests cannot be filtered by specific processes.
For example, if we set DescribeProcess or Execute permission on this service, the access is global for every process under this WPS service.

On the other hand, WPS-REST can have very granular permissions because of the route-based ServiceAPI implementation. This makes it impossible for 'corresponding' processes to have similar permissions.

ServiceWPS should be extended in order to provide child resources of type Process that would be allowed under the service. Permissions set directly on the service would behave as before (all or nothing), while specific permissions on a process would allow it to be described/executed.