Properly support plain text templates
Until recently YAMM worked O.K. with plain-text drafts. It would create an unnecessary HTML alternative, but everything otherwise worked fine. A couple of weeks ago, the HTML alternative created by YAMM was broken (missing all line breaks), making it effectively impossible to use a plain text drafts as a YAMM template.
YAMM should support sending plaint-text email from a plain text draft template:
If a plain text draft is selected as the template in YAMM, the resulting merged messages should be sent out as plain text email with NO HTML alternative.
Normal Gmail line-wrapping should apply (so messages all have lines of no more than ~75 characters long).
Template substitution should work as usual, with the proviso that substituted values be converted to plain text if required.