add link to structured data

- add link to TextProperty, not only 'name'
- add external link to 'url'
- add link to DateTime, fixing previous type error
Merge branch 'ADD-link-to-structured-data' of https://github.com/jangxyz/ecogwiki into jangxyz-ADD-link-to-structured-data
Do not treat TextProperty as a link
Merge branch 'jangxyz-ADD-link-to-structured-data'