exclude 'hidden' (deleted) simpledata items from api outputs fixes #528
added new all_as_list() to revisionable model

also fixed tests in line with new hidden field
slightly change the way all_active() works so that further filtering can be applied before calling ->get(). this allows us to avoid overriding the all_as_list method in revisionable.
Merge pull request #553 from unikent/bugs/deleted_awards_not_being_removed

exclude 'hidden' (deleted) simpledata items from api outputs