[dwm] Wiki date format

I suggest to change the date format (on the entry page) into
yyyy-mm-dd. The current format is confusing because you never know if
it is dd/mm/yyyy or mm/dd/yyyy. To solve this problem and to provide a
sane date format that works well with ``computer logic'', the ISO 8601
was created.

Please consider using yyyy-mm-dd.

See:
http://en.wikipedia.org/wiki/Calendar_date#Usage_issues
http://en.wikipedia.org/wiki/ISO_8601

meillo