Change default theme to System Default (#2608)

* Change default theme to System Default

Hopefully this was the only string that dictated the default setting.

* Update PreferencesHelper.kt

app/src/main/java/eu/kanade/tachiyomi/data/preference/PreferencesHelper.kt

@@ -54,7 +54,7 @@ class PreferencesHelper(val context: Context) {
 
     fun clear() = prefs.edit().clear().apply()
 
-    fun themeMode() = rxPrefs.getString(Keys.themeMode, Values.THEME_MODE_LIGHT)
+    fun themeMode() = rxPrefs.getString(Keys.themeMode, Values.THEME_MODE_SYSTEM)
 
     fun themeDark() = prefs.getString(Keys.themeDark, Values.THEME_DARK_DEFAULT)
 

app/src/main/java/eu/kanade/tachiyomi/ui/setting/SettingsGeneralController.kt

@@ -71,7 +71,7 @@ class SettingsGeneralController : SettingsController() {
                         Values.THEME_MODE_LIGHT,
                         Values.THEME_MODE_DARK)
             }
-            defaultValue = Values.THEME_MODE_LIGHT
+            defaultValue = Values.THEME_MODE_SYSTEM
             summary = "%s"
 
             onChange {