Add listing streams by Channels.

Added functionality for listing streams sorted by amount of viewers,
as seen when clicking "Channels" on twitch.tv. I don't actually know
any of the supported languages except English. The strings for other
languages were taken from the Twitch.tv site, by changing the site's
language. However, I couldn't find Czech on Twitch.tv, so it uses
Google Translate.

I don't know of the naming convention used in the localization files,
so I just gave the string ID 30008.