Add [-a|--app CODE] parameter to docker:create command

To enable one line installation with the new boilerplate stucture (using "app" instead of "code"-dir), an additional parameter "--app" (beside "--code") is needed.

After adding it, it could be used like this:
ct docker:create --docker=typo3 --app=git@bitbucket.org:projectname/app.git projectname

[josefglatz]

Could you please create a PR for it?

[kitzberger]

Maybe simple switch it entirely from code to app? And/or how about making it configurable via a news setting in /etc/clitools.ini whether to use code or app?

[josefglatz]

We have actually old and new boilerplates running next to each other. Hmmm

What about adding both?

[josefglatz]

on it