Added new Event_type page

Lists all possible event_types as controlled vocabulary.
Update 2014-05-06-event-type-list.markdown
Added link to even-type-list page
Updated text
Update 2013-08-21-trade-events.markdown
Updated 2013-08-21-trade-events.markdown
Merge pull request #5 from InternationalTradeAdministration/Stuart-05-06

Stuart 05 06 - Added event_type page