Add support for opsgenie tags and source

-override alert source field in config
-add static tags in config
-enable OverwriteQuietHours tag for critical alerts in config
-add event status tags "warning" or "critical"
added generic command check
moved elasticsearch related plugins to the proper directory
Merge pull request #174 from lapresse/fix-es

moved elasticsearch related plugins to the proper directory
improved description
Merge pull request #172 from pumpkineater/master

Opsgenie handler enhancements
Merge pull request #173 from lapresse/check-cmd

added generic command check