Display item links in HTML/RDFa view and fix some general issues

- Add items to resource UI template (adds links to details, see #82)
- Fix missing entries when many values are expected but one occurs
- Remove distinction between multi and single values in templates
- Display only existing values in the RDFa table (no '--' entries)

Samples:

http://api.lobid.org/resource?id=0940450003&format=page
http://api.lobid.org/person?name=Johann+Sebastian+Bach&format=page