Load the themes into the Tkinter interpreter

def _load_themes(self):
        """Load the themes into the Tkinter interpreter"""
        with utils.temporary_chdir(utils.get_file_directory()):
            self._append_theme_dir("themes")
            self.tk.eval("source themes/pkgIndex.tcl")
            theme_dir = "gif" if not self.png_support else "png"
            self._append_theme_dir(theme_dir)
            self.tk.eval("source {}/pkgIndex.tcl".format(theme_dir))
        self.tk.call("package", "require", "ttk::theme::scid")