Allow to search for factoids

This has been asked for many times in IRC. Attached patch implements a simple, GET-based search form that optionally adds a case-insensitive WHERE clause to the query.

By using GET, the search query is passed on to pager links. Unfortunately, FAPI does not support _validate and _submit functions for GET-based forms yet, so we need to manually check whether the Reset button has been pushed.

Cool?