expose fewer internals in packages, for easier software reuse

- prometheus is now behind an interface, they aren't dependencies for the
  reusable components anymore.
- some dependencies have been inverted: instead of packages importing a main
  package to get configuration, the main package now sets configuration in
  these packages. that means fewer internals are pulled in.
- some functions now have new parameters for values that were retrieved from
  package "mox-".

webmail/api.go

@@ -557,8 +557,9 @@ func (w Webmail) MessageSubmit(ctx context.Context, m SubmitMessage) {
 	var msgPrefix string
 	fd := fromAddr.Address.Domain
 	confDom, _ := mox.Conf.Domain(fd)
-	if len(confDom.DKIM.Sign) > 0 {
-		dkimHeaders, err := dkim.Sign(ctx, log.Logger, fromAddr.Address.Localpart, fd, confDom.DKIM, smtputf8, dataFile)
+	selectors := mox.DKIMSelectors(confDom.DKIM)
+	if len(selectors) > 0 {
+		dkimHeaders, err := dkim.Sign(ctx, log.Logger, fromAddr.Address.Localpart, fd, selectors, smtputf8, dataFile)
 		if err != nil {
 			metricServerErrors.WithLabelValues("dkimsign").Inc()
 		}

webmail/message.go

@@ -13,8 +13,8 @@ import (
 	"github.com/mjl-/mox/dns"
 	"github.com/mjl-/mox/message"
 	"github.com/mjl-/mox/mlog"
+	"github.com/mjl-/mox/mox-"
 	"github.com/mjl-/mox/moxio"
-	"github.com/mjl-/mox/moxvar"
 	"github.com/mjl-/mox/smtp"
 	"github.com/mjl-/mox/store"
 )
@@ -39,7 +39,7 @@ func tryDecodeParam(log mlog.Log, name string) string {
 		return name
 	}
 	// todo: find where this is allowed. it seems quite common. perhaps we should remove the pedantic check?
-	if moxvar.Pedantic {
+	if mox.Pedantic {
 		log.Debug("attachment contains rfc2047 q/b-word-encoded mime parameter instead of rfc2231-encoded", slog.String("name", name))
 		return name
 	}