Replace restic.Progress with new progress.Counter

This fixes two race conditions while cleaning up the code.

internal/ui/progress/signals_sysv.go

@@ -0,0 +1,12 @@
+// +build linux solaris
+
+package progress
+
+import (
+	"os/signal"
+	"syscall"
+)
+
+func setupSignals() {
+	signal.Notify(signals.ch, syscall.SIGUSR1)
+}