[hotfix/open_option_no_default] Adding placeholder to command option

If the default value of the option at a command is null, you can set the placeholder that will be the value displayed by default.

before:
  --open="", -o  Open a url of default system in the preferred application

after:
  --open="application", -o  Open a url of default system in the preferred application
[hotfix/open_option_no_default] Fixing option --open in command `start/restart` not null
[hotfix/open_option_no_default] update CHANGELOG
Bumped version number to 0.8.1
Merge branch 'hotfix/open_option_no_default'
Bumped version number to 0.8.2
Fixing downloading requireds keys to connect docker. #208
Merge branch 'hotfix/sftp_error'