Issue 1002 : Updated api/users

This follows the details specified at https://github.com/MarkUsProject/Markus/issues/1002 

Quick overview:
-api/users now uses :id for show and update methods
-limit, offset and filter parameters are available for retrieving collections (index method)
-the filter parameter is available to show and index methods to restrict which attributes are returned for each resource
-The changes do not conflict with any of the other current API routes