Several minor updates (incomplete)

* Enabled bcrypt-ruby in Gemfile
* Added editor_user_id to articles and comments tables and migrated
* Updated fixtures to refer to each other rather than to id numbers for
  certain elements with interrelationships
Continuation of minor updates

* Updated articles/users index/show erbs to refer properly to users and
  security_levels by name/number as appropriate instead of by id
* Still needs updating of _form erb to allow drop-down selection of same
* Previous commit included some of these changes (uncatalogued in that
  commit text)