ome-xml: Add joda-time 2.2 as a build dependency
ome-xml: Timestamp uses Joda Instant and DateTime internally for ISO-8601 dates

Internal timezone representation: UTC in milliseconds (Instant)
Input timezone representation: Defined in ISO-8601 string
Output timezone representation: UTC

The date handling is made reproducible and consistent by using UTC
everywhere.  If it's a non-UTC date on input, we convert to UTC.

The input and output of native Java Date and Calendar types is not
currently affected; we don't convert to UTC in input, but this is
an amendment which should be considered.