This reverts commit 303f79f8.

This reverts commit d66148ef, reversing
changes made to cdb64a81.

This change needed to be reverted,
because not enough email clients support inline images.

This adds the functionality of replacing all images that were uploaded
to gitlab with inline images(base64) in emails.
This change fixes the broken images in emails that 7.8 introduced

Rationale:

* In this notification email, the message is the most important content.
It should not be dimmed or smaller than the rest of the text.

* Now that all UI elements are removed, the message *is* the email. It
should be written as a standard email message, without styling.

Rationale: the author name is now displayed in the email "From" field;
this information is no longer needed.