Refactoring and proper handling of quantization.

Moving color and dithering related helpers into dedicated file.
In case of 2bpp (i.e. file generated from JPG), we don't apply any color
adjustments. In other cases, they are applied based on selected
algorithm.

lib/JpegToBmpConverter/JpegToBmpConverter.cpp

@@ -7,8 +7,7 @@
 #include <cstdio>
 #include <cstring>
 
-#include "Bitmap.h"
-#include "Dithering.h"
+#include "BitmapHelpers.h"
 
 // Context structure for picojpeg callback
 struct JpegReadContext {
@@ -356,7 +355,7 @@ bool JpegToBmpConverter::jpegFileToBmpStream(FsFile& jpegFile, Print& bmpOut) {
           }
         } else {
           for (int x = 0; x < outWidth; x++) {
-            const uint8_t gray = mcuRowBuffer[bufferY * imageInfo.m_width + x];
+            const uint8_t gray = adjustPixel(mcuRowBuffer[bufferY * imageInfo.m_width + x]);
             uint8_t twoBit;
             if (atkinsonDitherer) {
               twoBit = atkinsonDitherer->processPixel(gray, x);