Merge NGDC and GitHub versions UnidataDD2MI.xsl 

Integration of NGDC modifications. These have been tested on IOOS metadata since July of this year. 
This is a summary: 
* 2014-11-25. fixed error that was outputting '::' at the end of a date.
* 2014-07-24. test for null date and fixed another seconds since.... input. Translates UTC dates to ISO dateTime and 8601 basic dates to 8601 extended.
* 2014-07-17. updated dimensionResolution to handle many but not all ISO 8601 durations*
* 2014-07-16. updated uom units for time to display only seconds or days when includes "days since..." or "seconds since..." text. 
* 2014-04-19. Changed order to look in CFMetadata group first in *unit variables. Added normalize-space dimensionResolution param to fix vertical units error. 
* 2012-05-11. 2.3 (slight revision): Changed the attribute name from coverage_type to coverage_content_type to be more correct and directly comparable to ISO....