Replace custom date format by international standard

[wesley-petit]

In Sunlight, a date is required to read the sun's position from a csv file generated by the [SunEarthTools] website (https://www.sunearthtools.com/dp/tools/pos_sun.php?lang=fr).

The Sunlight date is a custom format for 3DUSE, converting the timestamp into hours. For example, 2016-01-01 at 00:00 corresponds to 1 451 602 800 seconds in the timestamp and 1 451 602 800 / 3600 = 403 223 in the 3DUSE format.

To follow UD-SV's guidelines for standards and ease of use, it would be useful to replace the custom format with an international input format such as ISO-8601 or with the timestamp directly.