rename misleading 'new_guy' variable to 'new_app'
remove the default 'list' task for the 'apps' subcommand

Ideally we would keep 'list' as the default task for the 'apps'
subcommand, but right now, this bug in thor means that default_task
breaks subcommand help:

  https://github.com/wycats/thor/issues/306

so it's probably better to leave it out for now.
add missing json dependency to ensure to_json is available