Implementation of Spatial Scope/Priority Datasets codelists in GeoNetwork

**Bug Description**
When using description 'Example on how to use the GeoNetwork editor' (see: https://webgate.ec.europa.eu/fpfis/wikis/display/InspireMIG/Example+on+how+to+use+the+GeoNetwork+editor) in GeoNetwork (3.6.0.0) to fullfill technical implementation (see: https://webgate.ec.europa.eu/fpfis/wikis/display/InspireMIG/Spatial+scope+code+list) for tagging data sets with the Spatial scope code list from INSPIRE metadate code list register we discovered several problems:

1. GeoNetwork Editor encodes the values of the codelist in metadata-xml using locally stored *.rdf file instead of using the link to INSPIRE Registry where official codelist is stored

XPath: /gmd:MD_Metadata/gmd:identificationInfo/gmd:MD_DataIdentification/gmd:descriptiveKeywords[6]/gmd:MD_Keywords/gmd:thesaurusName/gmd:CI_Citation/gmd:identifier/gmd:MD_Identifier/gmd:code/gmx:Anchor/@xlink:href

2. Metadata element attribute @xlink:href (../gmd:identifier/gmd:MD_Identifier/gmd:code/gmx:Anchor/@xlink:href) is encoded inside the gmx:Anchor element even though we are using the gco_CharacterString in Editor (“gear icon” button) for the encoding.
Both encodings are supported in the technical implementation.

3. Metadata element gmd:CI_DateTypeCode must have publication value inside the xml-tag according to technical implementation and Geonetwork doesn’t encode the value inside the xml-tag

These points lead to difference in XML Metadata encoding and the technical implementation description. (see attached images)

[SpatialScopeInGeonetworkWithGMXAnchor.txt](https://github.com/geonetwork/core-geonetwork/files/3385964/SpatialScopeInGeonetworkWithGMXAnchor.txt)
[SpatialScopeInGeonetworkWithGCO.txt](https://github.com/geonetwork/core-geonetwork/files/3385965/SpatialScopeInGeonetworkWithGCO.txt)

**Steps to Reproduce:**

1. Use GN 3.6.0.0
2. Reproduce the description from https://webgate.ec.europa.eu/fpfis/wikis/display/InspireMIG/Example+on+how+to+use+the+GeoNetwork+editor
3. Compare XML Metadata encoding from GN and technical implementation from https://webgate.ec.europa.eu/fpfis/wikis/display/InspireMIG/Spatial+scope+code+list

gmx:Anchor

gco:CharacterString

Start with the GeoNetwork editor reproduction steps for GN 3.6.0.0 and inspect the XPath for the spatial scope codelist identifier. Compare the generated metadata with the linked INSPIRE implementation, and consider the issue done when the registry href, permitted Anchor or CharacterString encoding, and publication date value match the stated requirements.

Written by the indexing model from the issue text.