Add new sound from the front-end

Add an icon where sounds can be dropped on (or the url can be entered). The frontend picks up the url and sends it to the server. The server downloads the file (maybe add some file size limit, or time limit), transcodes it to wav (using mpg321 for example), normalizes it and adds it to the collection

Possibly make this authorized so we're not flooded with 10h nyancat sounds
