Use .gaku in the project dir as the last fallback

In case the user doesn't care to place .gaku in a sane place, let's make
it possible to also set configuration by altering the project directory
.gaku file directly.
Raise default initial distance to 8

This is what the default was anyway should there be no config file. It
makes no sense for the default config file and the fallback to differ.
Further guard against weird config
Tell user what to do when no decks are found