SSDM-13926: Writing tests for import/export API. Created separate test classes for uncompressed import and for ZIP import.

SSDM-13843: Added a fix for properties that contain both a value and a link to a controlled vocabulary term.

SSDM-13579: Added a check in the pre-flight requests (OPTIONS) branch, which is required for a DELETE request. This is to make it do a real request check instead of merely accepting everything.

SSDM-13579: Made the server accept pre-flight requests (OPTIONS), which is required for a DELETE request.