Fix guestbook entry edit, some unwanted fields were also updated

This seems to be an old one, but it still exists.

Editing guestbook entry overrides `btGuestBookEntries`.`uID` with current user `uID`. Because of that editor is now shown as poster of that entry.

`entryDate` was defined as `deftimestamp` causing field to be updated with current timestamp on update. Entries are sorted by that field and edited field was lifted to first on list. Now it is saved only while adding entry.