repair pack: extract the repair logic into the repository package

Currently, the cmd/restic package contains a significant amount of code
that modifies repository internals. This code should in the mid-term
move into the repository package.

internal/ui/progress/printer.go

@@ -0,0 +1,30 @@
+package progress
+
+// A Printer can can return a new counter or print messages
+// at different log levels.
+// It must be safe to call its methods from concurrent goroutines.
+type Printer interface {
+	NewCounter(description string) *Counter
+
+	E(msg string, args ...interface{})
+	P(msg string, args ...interface{})
+	V(msg string, args ...interface{})
+	VV(msg string, args ...interface{})
+}
+
+// NoopPrinter discards all messages
+type NoopPrinter struct{}
+
+var _ Printer = (*NoopPrinter)(nil)
+
+func (*NoopPrinter) NewCounter(description string) *Counter {
+	return nil
+}
+
+func (*NoopPrinter) E(msg string, args ...interface{}) {}
+
+func (*NoopPrinter) P(msg string, args ...interface{}) {}
+
+func (*NoopPrinter) V(msg string, args ...interface{}) {}
+
+func (*NoopPrinter) VV(msg string, args ...interface{}) {}