User management interceptor

* Proxy service callback appender to allow the proxy configuration depends on dependencies added
* New callback for the user management
* Configurable with scripts for LDAP/FTP integration
* Disabled by default
* Configurable in the property overrider

By default no user interceptor is configured. To enable it:

* compile the project with `-PuserInterception`
* configure it with the property overrider options (commented)

Wiki page with some more information: https://github.com/geosolutions-it/OpenSDI-Manager2/wiki/User-Creation-Interceptor