Full ISO 8601 (RFC 3339 profile) compliance

[ypid]

ISO 8601 is the standard. There might currently still be other legacy date and time formats displayed by this library and the evaluation tool. Those should be changed to ISO 8601 regardless of the language.

This is the exact profile I propose:

Mon 2020-11-23 21:34:23

This does not change the opening hours syntax of course as that is defined in the spec. There have been discussion about designing the spec around ISO 8601 but this was not really doable, see https://wiki.openstreetmap.org/wiki/Talk:Key:opening_hours#International_standard_for_date_and_time

Example:

but will open tomorrow, 24 November, in 12 hours and 33 minutes.

Should become:

but will open tomorrow, 2020-11-24, in 12 hours and 33 minutes.

Or write ISO 8601 durations, at least in parenthesis as addition.

Related: #322