Add option to save a message

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
open_reply: fallback to use addr.local if addr.name is nil

If address doesn't contain name we end up with " wrote:" as a reply
header. It doesn't look nice.

Let's use addr.local + "@" if name is not defined. If addr.local is not
defined too, let's just use "somebody".

Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Use /usr/sbin/sendmail as a default

It's confusing that we don't have a default sendmail program. Let's use
/usr/sbin/sendmail as reasonable default.

Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Introduce g:notmuch_rb_folders_count_threads

If the option set, folders list shows count of threads, not messages

Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>