Settings : use enums instead of ints to store colors. Group all PTS settings into a struct.

PTS/SettingsPTS : Convert to/from LVGL color and Settings::Color, add functions to reduce code duplication.
Adapt SettingPineTimeStyle with the last Screen Interface

src/displayapp/Colors.h

@@ -0,0 +1,10 @@
+#pragma once
+
+#include <lvgl/src/lv_misc/lv_color.h>
+#include <components/settings/Settings.h>
+
+namespace Pinetime {
+  namespace Applications {
+    lv_color_t Convert(Controllers::Settings::Colors color);
+  }
+}