use different style for the heartrate settings and fix issues with settings file

src/components/settings/Settings.cpp

@@ -8,7 +8,6 @@ Settings::Settings(Pinetime::Controllers::FS& fs) : fs {fs} {
 }
 
 void Settings::Init() {
-
   // Load default settings from Flash
   LoadSettingsFromFile();
 }

src/components/settings/Settings.h

@@ -320,6 +320,7 @@ namespace Pinetime {
 
         Controllers::BrightnessController::Levels brightLevel = Controllers::BrightnessController::Levels::Medium;
 
+        // The interval for measuring the heart rate when the screen is off (in seconds)
         uint32_t heartRateBackgroundMeasurementInterval = 0;
       };