Fix initialization of Macro Columns setting and revery sticky temps

The Macro Columns setting was being stored as an unsigned char
when it should have been signed.  This caused the panel to try
and display 255 columns.

Also reverted the "sticky temp" feature for now.  This feature
saved the last temp a heater was set at when it was turned off
to allow easy restoral. Unfortunately, that's different than
what the DWC does.  Will consider re-adding it with a setup
option to control it at a later date.

src/PanelDue.cpp

@@ -146,7 +146,7 @@ struct FlashData
 	uint32_t colourScheme;
 	uint32_t brightness;
 	uint8_t displayDimmerType;
-	uint8_t macroColumns;
+	int8_t macroColumns;
 	uint8_t padding[2];
 	char dummy;								// must be at a multiple of 4 bytes from the start because flash is read/written in whole dwords
 
@@ -236,7 +236,9 @@ bool FlashData::IsValid() const
 		&& brightness <= Buzzer::MaxBrightness
 		&& language < UI::GetNumLanguages()
 		&& colourScheme < NumColourSchemes
-		&& displayDimmerType < (uint8_t)DisplayDimmerType::NumTypes;
+		&& displayDimmerType < (uint8_t)DisplayDimmerType::NumTypes
+		&& macroColumns >= -1
+		&& macroColumns <= 4;
 }
 
 bool FlashData::operator==(const FlashData& other)
@@ -562,7 +564,7 @@ int GetBrightness()
 	return (int)nvData.brightness;
 }
 
-void SetMacroColumns(uint8_t columns)
+void SetMacroColumns(int8_t columns)
 {
 	nvData.macroColumns = columns;
 }

src/PanelDue.hpp

@@ -59,7 +59,7 @@ extern FirmwareFeatures GetFirmwareFeatures();
 extern const char* array CondStripDrive(const char* array arg);
 extern void Reconnect();
 extern void Delay(uint32_t milliSeconds);
-extern void SetMacroColumns(uint8_t columns);
+extern void SetMacroColumns(int8_t columns);
 extern int GetMacroColumns();
 
 // Global data in PanelDue.cpp that is used elsewhere

src/UserInterface.cpp

@@ -1475,7 +1475,7 @@ namespace UI
 	// Update an active temperature if it's valid
 	void UpdateActiveTemperature(size_t index, int ival)
 	{
-		if (index < MaxHeaters && ival > 0)
+		if (index < MaxHeaters)
 		{
 			UpdateField(activeTemps[index], ival);
 		}
@@ -1484,7 +1484,7 @@ namespace UI
 	// Update a standby temperature if it's valid
 	void UpdateStandbyTemperature(size_t index, int ival)
 	{
-		if (index < MaxHeaters && ival > 0)
+		if (index < MaxHeaters)
 		{
 			UpdateField(standbyTemps[index], ival);
 		}