split system event plugin

Original file is >3000 loc, containing 3 handlers, each of about 700 loc not sharing any code. Split makes it easier to maintain them. In dss 2.0 they are called handlers, so strarted to moved them into 'handler' folder

Build triggered.

Build finished. Tests PASSED. Build results available at: http://dsjenkins.cloudapp.net/jenkins/job/dSS%20MR/57/

Status changed to merged

mentioned in commit c7b78ec6