frontends (quick app): reformulate backend not running message + use "Libervia" instead of "SàT"

libervia/frontends/quick_frontend/quick_app.py

@@ -367,7 +367,9 @@ class QuickApp(object):
 
     def _bridge_eb(self, failure):
         if isinstance(failure, exceptions.BridgeExceptionNoService):
-            print((_("Can't connect to SàT backend, are you sure it's launched ?")))
+            print(
+                _("Unable to connect to the Libervia backend. Are you sure it's running?")
+            )
             sys.exit(C.EXIT_BACKEND_NOT_FOUND)
         elif isinstance(failure, exceptions.BridgeInitError):
             print((_("Can't init bridge")))