Add side button layout configuration while on reader (#147)

## Summary

Allow swapping the side button layout between *next page - prev page*
and *prev page - next page* while reading

src/activities/settings/SettingsActivity.cpp

@@ -9,7 +9,7 @@
 
 // Define the static settings list
 namespace {
-constexpr int settingsCount = 7;
+constexpr int settingsCount = 8;
 const SettingInfo settingsList[settingsCount] = {
     // Should match with SLEEP_SCREEN_MODE
     {"Sleep Screen", SettingType::ENUM, &CrossPointSettings::sleepScreen, {"Dark", "Light", "Custom", "Cover"}},
@@ -24,6 +24,10 @@ const SettingInfo settingsList[settingsCount] = {
      SettingType::ENUM,
      &CrossPointSettings::frontButtonLayout,
      {"Bck, Cnfrm, Lft, Rght", "Lft, Rght, Bck, Cnfrm"}},
+    {"Side Button Layout (reader)",
+     SettingType::ENUM,
+     &CrossPointSettings::sideButtonLayout,
+     {"Prev, Next", "Next, Prev"}},
     {"Check for updates", SettingType::ACTION, nullptr, {}},
 };
 }  // namespace