Item layout tweaking, hook up more assets.

Update layouts for items in both list and grid mode to reflect
latest UX.  Use new card background in grid mode, and apply gradient
treatment over thumbnails.

Visibly mark currently selected root.

Bug: 10510022
Change-Id: I36b290d7082b5cdfd7b3167df7d976032bc01bd6
diff --git a/res/layout/item_root.xml b/res/layout/item_root.xml
index e9cf3aa..ce97b57 100644
--- a/res/layout/item_root.xml
+++ b/res/layout/item_root.xml
@@ -17,17 +17,17 @@
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
     android:layout_height="wrap_content"
-    android:minHeight="?android:attr/listPreferredItemHeight"
+    android:minHeight="?android:attr/listPreferredItemHeightSmall"
     android:paddingStart="?android:attr/listPreferredItemPaddingStart"
     android:paddingEnd="?android:attr/listPreferredItemPaddingEnd"
     android:gravity="center_vertical"
-    android:orientation="horizontal">
+    android:orientation="horizontal"
+    android:background="@drawable/item_root">
 
     <ImageView
         android:id="@android:id/icon"
-        android:layout_width="@android:dimen/app_icon_size"
-        android:layout_height="@android:dimen/app_icon_size"
-        android:layout_rowSpan="2"
+        android:layout_width="@dimen/icon_size"
+        android:layout_height="@dimen/icon_size"
         android:layout_marginEnd="8dip"
         android:scaleType="centerInside"
         android:contentDescription="@null" />