Various theme picker fixes.

- Add Previous button to custom flow
- Seed custom flow with the currently applied bundled theme
- Use add drawable icon instead of text
- Add padding between checkbox and "Add current wallpaper"
- Show ripple background on "Tap to edit"

Fixes: 130763331
Fixes: 130753131
Fixes: 130761402
Fixes: 130759176
Bug: 130759508
Test: visual
Change-Id: Ia82344befe8ac45489646d840453a71e31c83eae
diff --git a/res/layout/custom_theme_option.xml b/res/layout/custom_theme_option.xml
index b249555..09bd58e 100644
--- a/res/layout/custom_theme_option.xml
+++ b/res/layout/custom_theme_option.xml
@@ -34,13 +34,11 @@
         android:paddingHorizontal="@dimen/option_tile_padding_horizontal"
         android:paddingVertical="@dimen/option_tile_padding_vertical"
         android:background="@drawable/option_border">
-        <TextView
+        <ImageView
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:layout_gravity="center"
-            android:textSize="@dimen/theme_option_add_size"
-            android:textAlignment="center"
-            android:textColor="?android:colorAccent"
-            android:text="@string/add_custom_theme"/>
+            android:src="@drawable/ic_add_24px"
+            android:tint="?android:attr/colorAccent" />
     </FrameLayout>
 </LinearLayout>