Add i18n messages for the new 'wikibase-property' datatype

* wikibase-listdatatypes-wikibase-property-head
* wikibase-listdatatypes-wikibase-property-body
mostly copied from the respective 'wikibase-item' equivalents

Also added as comments on SpecialListDatatypes::execute().

Reported by GZWDer on Wikidata:
https://www.wikidata.org/wiki/?oldid=182136236#MediaWiki_message_requests

Change-Id: I83a8fed4f3e7395caa2b83201682bc911c99c6ef
Merge "Add i18n messages for the new 'wikibase-property' datatype"