Minor fixes to get_dataset:
*  Added `@imports` calls for the methods that need it.
*  Added, but commented out, tests that involve the API for get_dataset.
Fixes to `get_download`, commented out the API-dependent tests.
- added `@import` indicators for the `get_download` methods.
- pulled the single `download` out of a list and assigned it to a `download` class.
Undid the change to `get_download` for a single site.  Should have tested it first!