Call UAPI from WHM-api

It's important to preserve the possibility to call User's API from WHM's API.

Since API1 / API2 are deprecated and they'll be dismissed in the future, we need a to have a function in whmapi v1 in order to call the cPanel UAPI set of functions.

This will:

- speed up the adoption of UAPI and the the abandonment of old API1/2 functions

- preserve the possibility to fully integrate WHM with portal and reseller templates

- preserve performace (as it is you need to use a combination of the single sign to generate a user session key and then call the UAPI call with that key)