Retrieve full records in the CSW harvester and unify the record parsing with the GeoNetworkQ harvester.

Created by: adamreichold

Interestingly GeoNetwork's Q search API seems to just return the same CSW-based record format so that we can avoid parsing it twice. 🎉

We do have to switch XML parsers for now though, as the current version of quick-xml is unable to handle the namespacing employed in these formats. serde-xml-rs is measurably slower, but being incorrect and fast is relatively useless. It should also be straight forward to switch to another serde-based XML parser in the future, e.g. a fixed version of quick-xml. (This is also really only relevant if the XML parser actually becomes a performance bottleneck in the future.)

Fixes #49 (closed)