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/loggers.cc

@@ -1,5 +1,5 @@
 #include "loggers.hh"
-#include "../nix/progress-bar.hh"
+#include "progress-bar.hh"
 
 namespace nix {
 

src/nix-prefetch-url/nix-prefetch-url.cc

@@ -8,7 +8,7 @@
 #include "attr-path.hh"
 #include "finally.hh"
 #include "../nix/legacy.hh"
-#include "../nix/progress-bar.hh"
+#include "progress-bar.hh"
 #include "tarfile.hh"
 
 #include <iostream>