[ticket/12556][WIP]Custom Profile Field type date has inconsistent format

At the moment Custom Profile Field type DATE is saved in the DB
in the string format of d-m-Y where the leading zero to the days
and months are not written to DB.

The DB column in the DB is of the type VARCHAR.

This creates an issue when we want to search date range in the
Custom Profile Fields as the DB engine doesn't recognize the dates
as dates, but as arbitrary strings.

PHPBB3-12556