A simple structure representing a calendar date in UTC.
This class is deliberately extremely simple and delegates out to joda-time
for its actual functionality; it exists solely to abstract away our choice of
date and time library. (In JDK 8, it would probably make sense to use the new
standard library date and time classes.)
If you need to deal with multiple time zones or different calendars,
you're probably best served by using something more sophisticated (although the
from method in the companion object to convert from a org.joda.time.DateTime
will convert to UTC first).
Converts from DateTimeUTC to T, if an appropriate implicit conversion function is in scope