Add postpone command

This command uses the Postpone folder from the account config to save
messages to. Messages are saved as though they were sent so have a valid
'to' recipient address and should be able to be read back in for later
editing.

commands/msg/forward.go

@@ -70,7 +70,6 @@ func (forward) Execute(aerc *widgets.Aerc, args []string) error {
 		"To":      to,
 		"Subject": subject,
 	}
-
 	original := models.OriginalMail{}
 
 	addTab := func() (*widgets.Composer, error) {

commands/msg/reply.go

@@ -124,7 +124,7 @@ func (reply) Execute(aerc *widgets.Aerc, args []string) error {
 			original.Date = msg.Envelope.Date.Format("Mon Jan 2, 2006 at 3:04 PM")
 		}
 
-		composer, err := widgets.NewComposer(aerc, aerc.Config(),
+		composer, err := widgets.NewComposer(aerc, acct, aerc.Config(),
 			acct.AccountConfig(), acct.Worker(), template, defaults, original)
 		if err != nil {
 			aerc.PushError("Error: " + err.Error())

commands/msg/unsubscribe.go

@@ -90,6 +90,7 @@ func unsubscribeMailto(aerc *widgets.Aerc, u *url.URL) error {
 	}
 	composer, err := widgets.NewComposer(
 		aerc,
+		acct,
 		aerc.Config(),
 		acct.AccountConfig(),
 		acct.Worker(),