ActiveFedora#pid returns nil for new objects.
mark a test that required pid to return __DO_NOT_USE__ as pending.
convert some methods to private methods
require om >= 3.0.4
move application data to Hydrus, instead of mixing it into different models.
move some item methods into mixins.
trigger licenseable/versionable callback conditionally.
remove unused #toggle_hyphen_underscore
mixin contentable only into Hydrus::Item, and remove unused conditional checks for is_item/is_apo/is_collection
move default APO agreement into application config