Refactor image rendering and add Bluetooth setting

- Added logic to render images only in BW mode in Page.cpp.
- Implemented getRenderMode() in GfxRenderer.h.
- Increased SETTINGS_COUNT and added bluetoothEnabled field in CrossPointSettings.
- Updated saveToFile and loadFromFile methods to handle the new Bluetooth setting.
- Added Bluetooth toggle in SettingsActivity.

lib/GfxRenderer/GfxRenderer.h

@@ -83,6 +83,7 @@ class GfxRenderer {
 
   // Grayscale functions
   void setRenderMode(const RenderMode mode) { this->renderMode = mode; }
+  RenderMode getRenderMode() const { return renderMode; }
   void copyGrayscaleLsbBuffers() const;
   void copyGrayscaleMsbBuffers() const;
   void displayGrayBuffer() const;