emacs: Have email reply positions respect relevant message.el options

emacs: Have email reply positions respect relevant message.el options

Previously, when composing email replies with `notmuch-mua-new-mail',
the email signature would always be placed below the email citation.
However, there are two message.el user options that affect the
position of the signature and email body:
`message-cite-reply-position` and `message-cite-style-gmail'.
Previously, neither of these user options were respected.

Respect these user options. If `message-cite-reply-position' is
'traditional or 'below, place the email signature below the citation
(the previous behavior is retained). If `message-cite-reply-position'
is 'above, place the email signature above the citation (like in
Gmail-style email replies).

`message-cite-style-gmail' may specify a value for
`message-cite-reply-position'. If it does, that value takes precedence
over `message-cite-reply-position'.