[#53516641] Hdfs Datasets do not show "Import" and "Add workspace" links in the sidebar.

Hdfs datasets are now associated with only a single workspace via belong_to.
This contains a migration that moves existing "bound_workspaces" style associations
for hdfs datasets to the belong_to style.

Removed goofy "from_param" monkeypatch used in ModelMap. This was just an alias for 'find'.