Support searching resources by URN (see #78)

- Add `hasURN` property to `LobidResources.IdQuery`
- Add `hasURN` property to `views.tags.resource` template
- Add URN sample queries to index page template
- Add test data with `hasURN` properties and update tests
Merge pull request #161 from fsteeg/resource-by-urn

Support searching resources by URN