Add language search

[raxod502]

Currently you have to use ctrl-F to find the language you want, or scroll down manually, or type in the URL directly. This isn't the best experience, especially since the term you're searching for might not exactly match the canonical name of the language, which is what Riju uses.

If we introduce a search box for filtering languages, then that could index on aliases and language IDs as well as canonical language names, which would improve discoverability.