Relax ActiveRecord dependency: from 3.0 onwards
Missing ActiveSupport requirement
Rails 3.x compatible

ActiveRecord 4.x ::all method returns relation and replaces former
::scope method.  However `::where(nil)` works across versions.

See: http://stackoverflow.com/q/18198963/304175
Remove unused SaferTokens::Model

Orphaned remnant of some unknown idea.
Use Module::autoload