make "follow system" default for dark theme

Signed-off-by: tobiasKaminsky <tobias@kaminsky.me>

src/main/java/com/nextcloud/client/preferences/AppPreferencesImpl.java

@@ -414,10 +414,10 @@ public final class AppPreferencesImpl implements AppPreferences {
     @Override
     public DarkMode getDarkThemeMode() {
         try {
-            return DarkMode.valueOf(preferences.getString(PREF__DARK_THEME, DarkMode.LIGHT.name()));
+            return DarkMode.valueOf(preferences.getString(PREF__DARK_THEME, DarkMode.SYSTEM.name()));
         } catch (ClassCastException e) {
-            preferences.edit().putString(PREF__DARK_THEME, DarkMode.LIGHT.name()).apply();
-            return DarkMode.DARK;
+            preferences.edit().putString(PREF__DARK_THEME, DarkMode.SYSTEM.name()).apply();
+            return DarkMode.SYSTEM;
         }
     }
 

src/main/java/com/owncloud/android/ui/activity/SettingsActivity.java

@@ -711,8 +711,8 @@ public class SettingsActivity extends ThemedPreferenceActivity
         themePref.setEntryValues(themeValues.toArray(new String[0]));
 
         if (TextUtils.isEmpty(themePref.getEntry())) {
-            themePref.setValue(DarkMode.LIGHT.name());
-            themePref.setSummary(TextUtils.isEmpty(themePref.getEntry()) ? DarkMode.LIGHT.name() : themePref.getEntry());
+            themePref.setValue(DarkMode.SYSTEM.name());
+            themePref.setSummary(TextUtils.isEmpty(themePref.getEntry()) ? DarkMode.SYSTEM.name() : themePref.getEntry());
         }
 
         themePref.setOnPreferenceChangeListener((preference, newValue) -> {