Add functions to retrieve the users list in the User API

The user API available through $services.user provides various functions to manipulate users, including a function to check if a user exists or not, but no listing function.

The listing can be done using the $services.query API by whoever has the rights, but the user needs to know what query to provide to $services.query.

There should be an API in $services.user to do this listing, with parameters to:

• get all global or local users
• active / inactive users

In terms of rights, there is no reason for this new API to do more or less than the query API, it would just be a shortcut for the query API, so that the caller doesn't need to know the query to perform.