Fix sorting order

It is not possible to order by date given the current storage format
(text formatted by PHP's date("F j, Y - H:i") function)

This patch is a first fix for existing installations to order snippets
by ID (which is autoincrementing).

Another patch that will follow aim to additionnaly store the date in
an ISO 8601 format.
Merge pull request #25 from zertrin/fix-order

Thank you, I never checked in details for ordering, but it is proper this way.