Added Lexical Sort methods to finders

More often than not I find that I need the findAllSortedBy/fetchrequest to be sorted lexically (Finder-like sorting, for example "Item 1", "Item 2", …, "Item 10" instead of "Item 1", "Item 10", "Item 2",…) which is the current default.

So as not to break compatibility, I've added Lexical versions to all the findAllSortedBy: methods, which I've named findAllSortedLexicallyBy:.

Perhaps it might be useful to others too.