tag editor: add support for numerating tracks using xx/xx format

doc/config

@@ -290,6 +290,8 @@
 #
 #empty_tag_marker = "<empty>"
 #
+#tag_editor_extended_numeration = "no"
+#
 #enable_window_title = "yes"
 #
 ##

doc/ncmpcpp.1

@@ -246,6 +246,9 @@ If enabled, ncmpcpp will be able to delete files using its browser screen.
 .B allow_physical_directories_deletion = yes/no
 If enabled, ncmpcpp will be able to delete directories using its browser screen.
 .TP 
+.B tag_editor_extended_numeration  = yes/no
+If enabled, tag editor will number tracks using format xx/yy (where xx is the current track and yy is total amount of all numbered tracks), not plain xx.
+.TP
 .B enable_window_title = yes/no
 If enabled, ncmpcpp will override current window title with its own one.
 .TP