Major reform in the chat backend: use xotcl-core ORM to define all the relevant objects and data model
This greatly converges oracle and postgres codebase and will make easier to apply incremental updates to the data model in the future. It will also automatically update the acs_object_type metadata automatically
TODO: remove legacy procs, temporarly reimplemented using the new backend
Chat data-model reform: - introduce on delete cascade on foreign key constraints so package can be removed easily e.g. from the subsite UI - remove remaining stored procedures (and function_args definitions) to relieve the burden on the development process and reduce divergency between oracle and postgres code - converge oracle and postgres datamodels: . oracle -> add missing messages_time_window column . postgres -> remove creation_date from chat_transcripts, which was found to be still existing on old downstream installations