Better search ordering/ranking

Right now it looks like we list apps alphabetically in search results, regardless of their relevance to the search. Performing the same search with `appstreamcli` seems to return better ordering, so if we can use that, we probably should—otherwise (or if we find it produces better results), we should order results by:

>- App names starting with the term
>- App names containing the term
>- Everything else

…as mentioned by @WatchMkr in https://github.com/pop-os/shop/issues/171