statusline: make statusline folder-specific

Make statusline folder-specific. Update filter, search and threading
status when changing folders.

Commit 2512c04 ("statusline: implement per-account status") introduced
an account-specific statusline. This makes it account- and
folder-specific.

Signed-off-by: Koni Marti <koni.marti@gmail.com>
Tested-by: Moritz Poldrack <moritz@poldrack.dev>

commands/account/cf.go

@@ -5,6 +5,7 @@ import (
 	"strings"
 
 	"git.sr.ht/~rjarry/aerc/commands"
+	"git.sr.ht/~rjarry/aerc/lib/statusline"
 	"git.sr.ht/~rjarry/aerc/widgets"
 )
 
@@ -52,6 +53,7 @@ func (ChangeFolder) Execute(aerc *widgets.Aerc, args []string) error {
 	store := acct.Store()
 	if store != nil {
 		store.ApplyClear()
+		acct.SetStatus(statusline.SearchFilterClear())
 	}
 	return nil
 }