api: add establish_db_connection helper
api: remove sinatra/json helper
api: include root in json respond from ActiveRecord objects
api(models): remove unused references to other models
api(models): add serializable_hash to models, to control json output
api(CollectionsController): update response because of introduction of root node
api(CollectionsController): namespace cleanup
api(CollectionsController): implement update action
api(CollectionsController): implement delete action
api: do not validate presence of Set.number as can be nil
api: change CardCollection into Collectionable
api: little cleanup and comments
api(application): fix forgotten reply_with_message
api(scripts): use MTGTRACKER_ENV to set activerecord environment
api(Collection): retrieve quantity with relation select
api(application): perform payload JSON parse also on delete
api(Sinatra::ErrorHandling): better 404 message
api(CollectionsController): add card modification endpoints
api(db): add seed scripts