new & opt.

- new: ssh discontinuity test
- opt.: server cmds
- opt.: check ssh client status before exec cmds
- new: #124 notify on discontinuity

lib/data/model/app/shell_func.dart

@@ -83,6 +83,7 @@ extension EnumX on Enum {
 }
 
 enum StatusCmdType {
+  time,
   net,
   sys,
   cpu,