add empty static tag array in the datadog config
Update datadog handler
 - Convert to class extending Sensu::Handler
 - Change message title to only include the check name, not the hostname
 - Add aggregation key based on message title
 - Set event source as nagios so that events can be claimed and weekly reports run
 - Allow static tags to be set in configuration
 - Add dynamic tags based on subscribers in the event
 - Set priority based on event status