Proposed change: replace java.util.Date with java.time.*

[James Agnew]

Hi All,

As mentioned during the 5.7.0 release webinar, our next release will be a major bump to 6.0.0.

One of the changes being considered as a part of this bump is to replace our use of `java.util.Date` in the datatype classes for date/dateTime/instant with their respective java.time equivalents. Presumably:

* date: java.time.LocalDate
* dateTime / instant: java.time.ZonedDateTime

This would be a breaking change since calling (for example) `DateTime#getValue()` would start returning a ZonedDateTime and not a Date. Presumably we would include utility method like `getValueAsDate()` and `setValueAsDate(Date)`.

So I guess the question here is: Are there any objections to this change? Or for that matter do people think this is beneficial enough to warrant the change?

Cheers,

James