DateTime support in DateFormatter. #476

[lemonboston]

@dmfs Could you please review the conversion and Time-DateTime equivalence check in the test extra thoroughly?
You know the domain better, to assess that this conversion is good for the project or not.

[dmfs]

your tests don't seem to validate the actual Time values, i.e. minute, day', etc. Also I think your all-day handling might be incorrect. When an event is allday the timezone should be set to UTC. I'm not exactly sure what DateTimereturns in that case, maybe it already returnsUTC`.

[lemonboston]

I've added checking the individual fields in the test.

Also updated conversion to use "UTC" for all-day. But please note/check that Time constructors are used in different ways in the project, so if I searched for them, both the paremterless and with the timezone, so this "UTC" as default didn't look totally consistent from the first look. But I haven't checked the details.

Also rebased on master.

Ready for check again.

[dmfs]

Works for me.

[dmfs]

Merging this despite the CI issue.