Adding new API functions: register_id_with_basename, unregister_id_with_basename, find_ids_from_basename; adding test

This patch introduces the following new API functions:

 - `register_id_with_basename`, `unregister_id_with_basename`  
 - `find_id_from_basename`, `find_ids_from_basename`, `find_all_ids_from_basename`

all of which help to simplify orchestrating collective operations.

This patch also fixes an issue with the automatic conversion of a `hpx::naming::gid_type` which was returned by an action into a proper `hpx::id_type` instance.