22.0-introduce_CREST_2-IOVDbSvc

Somehow managed to screw up original merge request ('detached head'?), so re-introducing this: Introduce classes allowing the IOVDbSvc to contact a CREST (RESTful, web-based) database and retrieve data from this source instead of oracle. The functionality of IOVDbSvc itself been extended to write to file, but not yet read from the CREST web service (although classes, and testing code, are in place to allow this in a future development). Additional changes will be made elsewhere to facilitate this, before returning to implement in this package.