Load further full-text search results if the user scrolls to the end

[Jaifroid]

trafficstars

We currently prioritize title search over full-text search results, because title search tends to be more accurate, and if we get enough title-search results, we might never actually load the ft ones. If the user scrolls to the end of the search list, we could load some more ft results (or do it if the user scrolls past the first half of results showing).

The downside is that calls to the libzim worker are currently somewhat "expensive" and noticeably slow even on powerful desktop machines. Is the extra CPU usage worth it when 99% of the time we get fast and accurate results within the first user-selectable window of results?