turned readCookie into private function
turned readCookie into private function

This is mainly to indicate that this is a utility function, not
disrupting the remaining code's readability.

If it is to be reused, it should be moved to a separate module.

FND/tiddlyspace,FND/tiddlyspace,FND/tiddlyspace,TiddlySpace/tiddlyspace,TiddlySpace/tiddlyspace,TiddlySpace/tiddlyspace