Changed EventTrigger class visibility to public,

This is required when extending EventGraph is neccessary as
EventTrigger instance is required as apart of the EventGraph constructor.
Merge pull request #346 from asaf/eventTriggerPublic

Changed EventTrigger class visibility to public,
hashCode implementation for Parameter class.

An existing implementation of Parameter.equals exist without
having an implementation of hashCode(), this violate the requirement
that equal must have an equal hashcodes.
GraphMLReader did not properly type cast properties.

Change the key type map so that it used the id per the graphml spec.
Upgraded to jackson 2 and fasterxml namespace. #350
Updated changelog.