Support linking to review searches

Add handling of URL parameters to /search, mapping "q<term>=<value>" to
"<term>:<value>" and "q=<value>" to "<value>".  When any such parameters
is supplied, /search renders with a single input field (containing the
resulting "quick search" query) and inlined search results.

Also add a link to such a URL in the "Search results" dialog opened for
quick searches (on any page) and regular searches on /search.