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/values/dimens.xml b/res/values/dimens.xml
index e5c4138..e5b5b4e 100644
--- a/res/values/dimens.xml
+++ b/res/values/dimens.xml
@@ -15,5 +15,8 @@
 -->
 
 <resources>
+    <dimen name="icon_size">32dp</dimen>
+    <dimen name="root_icon_size">24dp</dimen>
     <dimen name="grid_width">180dp</dimen>
+    <dimen name="grid_height">180dp</dimen>
 </resources>