Proper Media Type for JS files

I only got as far as `embed.js`...sadly.

Most `.js` files (at least) aren't getting any `Content-Type` set (nor `Content-Length`) for that matter. This is true with both the stock `.ini` files we provide.

I'm happy to dig into this more. This at least fixes `embed.js`'s media type.
Can you add an extra line break here as per PEP8?