[contactsd-birthday-plugin] reiterate further creating all day event for birthday

Continuing digging why birthday events behaved like they do.

Not sure yet if this is a proper pull request or a RFC / FYI. Need to anyway still continue investigating. Kind of also hoping someone would say I've understood something wrong, and restoring some faith in the calendar stack.

Alternatively could try to also fix sqlite side, if I've lost enough sanity already.