Metadata uuid from geonetwork

Fixes #1397.

@anguss00 Some thoughts about it:
 * Talk to POs a bit more about it. I had a discussion with @ggalibert
 * Looks like the references in geoserver to geonetwork can stay, but they should not affect portal
 * In terms of AODN, I think it's OK as well, because geonetwork is the point of truth, so if a record is in geonetwork, it will have an abstract/info
 * Possibly some cleanups in the DB side can be done, because we don't need to save the geonetwork URL WMS scanner will give us. @dnahodil, true?
 * Another step forward towards stateless

If it is decided to not use this PR for any reason, the function of `getFormattedMetadata` must be sanitized so it cannot call any random URL. As far as I saw there was no host verification in this function.

The `getFormattedMetadata` refactor is what we should aim for - a clean API which takes parameters on the server side, rather than double or triple encoded URLs that are assembled in JS.
I would suggest on the layer calling the field `metadataUuid`. You get the benefit of flattening but it makes it clear that the uuid is for the metadata record (and not the layer).