Use type aliases FilePath, FilePaths...

... for wxString and wxArrayStringEx, holding file paths (absolute or relative,
directory or plain file); to be replaced later with different types

(not yet using std::vector, becase of some uses of wxArrayString::Index with
two arguments)

src/AutoRecovery.h

@@ -105,7 +105,7 @@ public:
 
    bool IsEmpty() const;
 
-   bool Decode(const wxString & fileName);
+   bool Decode(const FilePath & fileName);
 
 private:
    void WriteName(const wxString & name);