[ticket/12655] Don't try to restore the definition in the help

PHPBB3-12655
Merge pull request #2543 from Nicofuma/ticket/12655

[ticket/12655] Run phpbbcli as a shell when --shell or -s is used

* Nicofuma/ticket/12655:
  [ticket/12655] Don't try to restore the definition in the help
  [ticket/12655] Fix coding style
  [ticket/12655] Make the --shell option available only for phpbbcli.php
  [ticket/12655] Fix coding style in \phpbb\console\application
  [ticket/12655] Set the arguments of \phpbb\console\application as required
  [ticket/12655] Don't require acp/common again in the commands
  [ticket/12655] Run the shell when --shell is used