cmd: add --progress-terminal-title to print ETA to terminal title

Adds a flag, --progress-terminal-title, that when used with --progress,
will print the string `ETA: %s` to the terminal title.

This also adds WriteTerminalTitle to lib/terminal

fs/accounting/stats.go

@@ -11,6 +11,7 @@ import (
 	"github.com/rclone/rclone/fs"
 	"github.com/rclone/rclone/fs/fserrors"
 	"github.com/rclone/rclone/fs/rc"
+	"github.com/rclone/rclone/lib/terminal"
 )
 
 // MaxCompletedTransfers specifies maximum number of completed transfers in startedTransfers list
@@ -282,6 +283,11 @@ func (s *StatsInfo) String() string {
 		xfrchkString,
 	)
 
+	if fs.Config.ProgressTerminalTitle {
+		// Writes ETA to the terminal title
+		terminal.WriteTerminalTitle("ETA: " + etaString(currentSize, totalSize, speed))
+	}
+
 	if !fs.Config.StatsOneLine {
 		_, _ = buf.WriteRune('\n')
 		errorDetails := ""

fs/config.go

@@ -107,6 +107,7 @@ type ConfigInfo struct {
 	StatsOneLineDateFormat string // If we want to customize the prefix
 	ErrorOnNoTransfer      bool   // Set appropriate exit code if no files transferred
 	Progress               bool
+	ProgressTerminalTitle  bool
 	Cookie                 bool
 	UseMmap                bool
 	CaCert                 string // Client Side CA

fs/config/configflags/configflags.go

@@ -110,6 +110,7 @@ func AddFlags(flagSet *pflag.FlagSet) {
 	flags.StringVarP(flagSet, &fs.Config.StatsOneLineDateFormat, "stats-one-line-date-format", "", fs.Config.StatsOneLineDateFormat, "Enables --stats-one-line-date and uses custom formatted date. Enclose date string in double quotes (\"). See https://golang.org/pkg/time/#Time.Format")
 	flags.BoolVarP(flagSet, &fs.Config.ErrorOnNoTransfer, "error-on-no-transfer", "", fs.Config.ErrorOnNoTransfer, "Sets exit code 9 if no files are transferred, useful in scripts")
 	flags.BoolVarP(flagSet, &fs.Config.Progress, "progress", "P", fs.Config.Progress, "Show progress during transfer.")
+	flags.BoolVarP(flagSet, &fs.Config.ProgressTerminalTitle, "progress-terminal-title", "", fs.Config.ProgressTerminalTitle, "Show progress on the terminal title. Requires -P/--progress.")
 	flags.BoolVarP(flagSet, &fs.Config.Cookie, "use-cookies", "", fs.Config.Cookie, "Enable session cookiejar.")
 	flags.BoolVarP(flagSet, &fs.Config.UseMmap, "use-mmap", "", fs.Config.UseMmap, "Use mmap allocator (see docs).")
 	flags.StringVarP(flagSet, &fs.Config.CaCert, "ca-cert", "", fs.Config.CaCert, "CA certificate used to verify servers")