Custom styling of email templates

Ping @beganovich Follow-up to issue #5185 - linebreaks in email templates. I can style quote/invoice PDF templates in the "includes" tab in the invoice designer. But there is no similar way to style email templates, and the editor is a little hard to use as the preview and final email often don't match. So as a workaround I did this: • go to settings > advanced settings > templates and reminders • choose an email template • populate the "Body" field as usual • at the end of the "Body" field, ALSO add a <style type="text/css">...</stye> tag, with styles that override defaults • now the preview is perfect But the actual sent email looks completely different. I think it's because the style tag is included in the email's source. But as you know that doesn't render properly, so before emails are sent their styles must be converted/embedded in the email's DOM…