MEM band optimization

1. Empty(defalut) station not tune
2. Change channel color for different status:
    Mem preview: Channel Empty → InsignificantColor , Exist → SignificantColor
    Mem storage:  Channel Empty → SignificantColor , Exist → InsignificantColor

src/constants.h

@@ -243,6 +243,10 @@ enum SPI_SPEED_ENUM {
   SPI_SPEED_COUNT
 };
 
+enum RADIO_MEM_POS_STATUS {
+  MEM_DARK, MEM_NORMAL, MEM_EXIST
+};
+
 static const uint8_t TEFLogo[] PROGMEM = {
   0xff, 0xff, 0xf8, 0x7f, 0xfe, 0x07, 0xff, 0xe0, 0xff, 0xff, 0xf8, 0xff, 0xff, 0x1f, 0xff, 0xe0,
   0xff, 0xff, 0xf9, 0xff, 0xff, 0x1f, 0xff, 0xe0, 0xff, 0xff, 0xfb, 0xff, 0xfe, 0x3f, 0xff, 0xe0,