fixed issues:
 - https://github.com/everit-org/jira-timetracker-plugin/issues/32
 - https://github.com/everit-org/jira-timetracker-plugin/issues/22
 - https://github.com/everit-org/jira-timetracker-plugin/issues/17
 - https://github.com/everit-org/jira-timetracker-plugin/issues/13