Move progress-bar.cc to libmain

Needed so that we can include it as a logger in loggers.cc without
adding a dependency on nix

This also requires moving names.hh to libutil to prevent a circular
dependency between libmain and libexpr

src/libmain/progress-bar.hh

@@ -0,0 +1,13 @@
+#pragma once
+
+#include "logging.hh"
+
+namespace nix {
+
+Logger* makeProgressBar(bool printBuildLogs = false);
+
+void startProgressBar(bool printBuildLogs = false);
+
+void stopProgressBar();
+
+}