Searching for titles is very slow due to additional grouping, joins and
sorting. Try to optimize some expensive queries and cache results.

Don't trigger too many searches from the web UI. Increase the delay before a search is launched from 100 to 500ms.

Change-Id: Ic87c11f6bc304b3e8e320fd021cb18a3a78e958e
Unshift the title search before the content_type condition, as this will
usually narrow down the selection faster, as there are less hits.