Don't show "active print" header if no printer is connected

CL-541

resources/qml/PrintMonitor.qml

@@ -106,6 +106,7 @@ Column
     {
         label: catalog.i18nc("@label", "Active print")
         width: base.width
+        visible: activePrinter != null
     }
 
 
@@ -114,6 +115,7 @@ Column
         label: catalog.i18nc("@label", "Job Name")
         value: activePrintJob != null ? activePrintJob.name : ""
         width: base.width
+        visible: activePrinter != null
     }
 
     MonitorItem
@@ -121,6 +123,7 @@ Column
         label: catalog.i18nc("@label", "Printing Time")
         value: activePrintJob != null ? getPrettyTime(activePrintJob.timeTotal) : ""
         width:base.width
+        visible: activePrinter != null
     }
 
     MonitorItem