Add Feishin desktop/web client and replace Sonixd

[repomansez]

Feishin is a pretty nice subsonic client made in TypeScript as a rewrite of Sonixd by the same developer, and it's not mentioned under clients, I've been using it and it happens to be the best client I've ever seen, so I think it deserves to take the place of Sonixd which is no longer maintained

Although it is under a new rewrite and we may have to change it again in the future, it's nowhere near ready yet, while Feishin is complete and up-to-date.

https://github.com/jeffvli/feishin