Embed shop logo in shop emails

[Algorithman]

Is your feature request related to a problem? Please describe.
The shop logo is added as a link to the homepage.
It would be nicer to add it as a embedded image (with content id and IsEmbedded=true)
I made some tests and it is easily done.

Change the header.liquid so it does add a src="cid:shoplogo" instead of the linked image to the page and then add a embedded attachment to the email with the contentId set & IsEmbedded=true if the shoplogo is present.