Zabbix

..F....... [DEV-641] fixed naming of dashboard-related files and actions

Controllers:
 - ControllerWidgetSystemView.php => CControllerWidgetProblemsBySvView.php

Views:
 - monitoring.widget.system.view.php => monitoring.widget.problemsbysv.view.php

Actions and widget types:
 - widget.syssum.view => widget.problemsbysv.view

Constants:
 - WIDGET_SYSTEM_STATUS => WIDGET_PROBLEMS_BY_SV

Widget names:
 - "System status" => "Problems by severity"