Icons for preference categories

app/src/main/res/xml/settings.xml

@@ -1,21 +1,27 @@
 <?xml version="1.0" encoding="utf-8"?>
 <PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
     <Preference
+        android:icon="@drawable/ic_settings_ethernet_black_36dp"
         android:key="preference_category_network"
         android:title="@string/settings_label_network"/>
     <Preference
+        android:icon="@drawable/ic_account_box_black_36dp"
         android:key="preference_category_identities"
         android:title="@string/pref_title_identities"/>
     <Preference
+        android:icon="@drawable/ic_visibility_black_36dp"
         android:key="preference_category_privacy"
         android:title="@string/pref_title_privacy"/>
     <Preference
+        android:icon="@drawable/ic_lock_black_36dp"
         android:key="preference_category_app_protection"
         android:title="@string/settings_label_app_protection"/>
     <Preference
+        android:icon="@drawable/ic_settings_display_black_36dp"
         android:key="preference_category_appearance"
         android:title="@string/settings_label_appearance"/>
     <Preference
+        android:icon="@drawable/ic_settings_black_36dp"
         android:key="preference_category_advanced"
         android:title="@string/settings_label_advanced"/>
 </PreferenceScreen>