refract cmd part

[roberChen]

current cmd related codes are not organized, it's better to refractor it using cobra

Known commands:

mindoc  install
        install and initialize  database
mindoc  -config string
        MinDoc configuration file.
mindoc  -dir string
        MinDoc working directory.
mindoc  -log string
        MinDoc log file path.
mindoc migrate
        migrate database[deprecated]
mindoc version
        print version info
mindoc service [install|remove|...]
        service mode
mindoc password -account <account_name> -password <pw>
       reset account password