config: #cleanup
mill-cli: protect against 'banner' not being configured
#doc #fix
Revert "config: #cleanup"

This reverts commit b49b15c8c05ddad0b4547f11826408b8f235593f.
config: add package.json to (end of) list of allowed config file names. that means if no papermill conf is found, we use package.json
package: update 'flatiron' dep