Removing unused method
Removing commented out code
First pass at re-implementing the Kit model

Extracting out a KitBuilder class, so the Kit class can just
be a lot simpler. For now, the ImmutableKit class is the
temporary replacement with the same interface as Kit, but when
all is said and done it will replace Kit completely.
Removing the old implementation of Kit

Good riddance!
Renaming ImmutableKit -> Kit and extracting to own file
Removing to_yaml() methods