IOMeters: rework initial display

Show a non highlighted string at the start of htop, not the failure
text.
Also the original fix only handled the text mode, not the bar mode.

Improves: 2977414d ("Discard stale information from DiskIO and NetworkIO meters")
Related: #860

Meter.h

@@ -134,6 +134,13 @@ typedef enum {
    LAST_METERMODE
 } MeterModeId;
 
+typedef enum {
+   RATESTATUS_DATA,
+   RATESTATUS_INIT,
+   RATESTATUS_NODATA,
+   RATESTATUS_STALE
+} MeterRateStatus;
+
 extern const MeterClass Meter_class;
 
 Meter* Meter_new(const ProcessList* pl, unsigned int param, const MeterClass* type);