WebSearch: resolve (internal) DOIs

• When accessing "CFG_SITE_URL/doi/foo/bar", try to resolve 'foo/bar' as DOI and return corresponding record (0247a:'foo/bar'). In this initial release the 'source' field (02472:doi) is not considered. (closes #1322)

Signed-off-by: Jerome Caffaro <jerome.caffaro@cern.ch>
Reviewed-by: Ludmila Marian <ludmila.marian@gmail.com>