always set valid dates, to avoid errors when strict mode is enabled on mysql

[davidegiunchidiennea]

If strict mode is enabled on mysql, the creation of aiowps's tables will fail with error:

MySQL: Invalid default value for 'event_date'

this is due to strict mode: https://stackoverflow.com/questions/36374335/error-in-mysql-when-setting-default-value-for-date-or-datetime?answertab=active#tab-top

To avoid it, always insert a valid date.

[Arsenal21]

Thank you. Can you by any chance resolve the conflict so I can take a proper look at this one.