Allow all %{variable} expansions in all strings
It doesn't make sense that %D is duration in some strings, but unrecognized in other cases.
e.g. I wanted to rename a set of file, but there were some name collisions because of poor tags. I wanted to use %d in the filename just to make them unique. But no, kid3 only replaces %d and %D in file->export. I smell some code duplication behind this user-interface inconsistency...
Imported from SourceForge, author: pcordes