Support dark mode in verification code keyboard.

app/src/main/res/layout/verification_pin_keyboard_view.xml

@@ -5,9 +5,9 @@
 
     <org.thoughtcrime.securesms.components.NumericKeyboardView
             android:id="@+id/keyboard_view"
-            android:keyBackground="@color/grey_300"
-            android:background="@color/grey_300"
-            android:keyTextColor="@color/black"
+            android:keyBackground="@color/signal_colorSurface1"
+            android:background="@color/signal_colorSurface1"
+            android:keyTextColor="@color/signal_colorOnSurface"
             android:shadowColor="@color/transparent"
             android:keyTextSize="30sp"
             android:elevation="3dp"