Getting really embed img

I'm sorry to say we here saw no difference between calling `->getMessageBody(...)` with parameter `$embeddedImg` set to `false` or to `true`.

I think I saw somewhere it has something to do with file saving somewhere and maybe replacing `cid:part-content-id` with the url where it has been saved.

We wanted "really embedded img", with `data:image` in the img `src` attribute, and so we did.

As a side note, thanks for your work on this project that takes all the pain off ! ;)