class library: improve Stethoscope redirection
The check whether server has SHM interface alone was not valid,
as it depended also on whether the server is running.
Remedy this issue and simplify redirection:
* change QtGUI key mapping:
'stethoscope' -> QStethoscope2
'stethoscope1' -> QStethoscope
* QStethoscope2: throw error if server not local
* Remove Stethoscope2 and redirection in Server:-scope, and implement
all redirection in Stethoscope: if GUI is Qt and server is running
and doesn't have SHM interface, redirect to QStethoscope, otherwise
use the 'stethoscope' key
* Add more defaults to Stethoscope arguments, to ease instantiation