restor `pomelo add` command && fix bugs

Change-Id: I3771633e36edb369d80c53efd7b3f82e6ca17cd7
* spawn child process: dev(not detached)/pro(detached) env

Change-Id: Id453258bf81935ec5a6cc012ad4c86f16fc57b85
update to 0.7.4

Change-Id: I7b6ce2f067992d96bc5b089c2104d48fd846fbe3