[libcontacts] Remove unnecessary sorting

When sorting is not required, clear the sort property of the fetch
request; the sorting does not cause errors, but results in unnecessary
effort to process the query.
[libcontacts] Ensure search terms are trimmed

When searching for merge candidates, trim the strings used as search
tokens in case they contain problematic whitespace.
Merge pull request #87 from matthewvogt/trim-search-terms

Minor improvements