Include : in time zone for ISO-8601 formatting

Addresses https://redmine.dataone.org/issues/4085#change-17448

Java 7 supports this formatting with the 'X' component (http://docs.oracle.com/javase/7/docs/api/java/text/SimpleDateFormat.html#iso8601timezone).
Since this is not available in Java 6, the SimpleDateFormatter objects are customized to insert a colon, courtesy http://stackoverflow.com/questions/2375222/java-simpledateformat-for-time-zone-with-a-colon-seperator/14422046#14422046
Merge pull request #392 from datadryad/dan-trello-9

Include colon (:) in time zone for ISO-8601 formatting