Add Style configuration

The following functionalities are added to configure aerc ui styles.
- Read stylesets from file with very basic fnmatch wildcard matching
- Add default styleset
- Support different stylesets as part of UiConfig allowing contextual
  styles.
- Move widgets/ui elements to use the stylesets.
- Add configuration manual for the styleset

commands/msg/forward.go

@@ -9,6 +9,7 @@ import (
 	"os"
 	"path"
 	"strings"
+	"time"
 
 	"git.sr.ht/~sircmpwn/aerc/models"
 	"git.sr.ht/~sircmpwn/aerc/widgets"
@@ -83,7 +84,7 @@ func (forward) Execute(aerc *widgets.Aerc, args []string) error {
 		composer, err := widgets.NewComposer(aerc, acct, aerc.Config(), acct.AccountConfig(),
 			acct.Worker(), template, defaults, original)
 		if err != nil {
-			aerc.PushError("Error: " + err.Error())
+			aerc.PushError("Error: "+err.Error(), 10*time.Second)
 			return nil, err
 		}