EP:
https://developer.atlassian.com/display/JIRADEV/Performing+Issue+Operations#PerformingIssueOperations-TransitioninganexistingIssue
https://developer.atlassian.com/static/javadoc/jira/5.0.5/reference/com/atlassian/jira/bc/issue/IssueService.html#validateTransition(com.atlassian.crowd.embedded.api.User, java.lang.Long, int, com.atlassian.jira.issue.IssueInputParameters)
https://answers.atlassian.com/questions/44508/programatically-modifychangeupdate-an-issues-status-in-java