First pass at new FolderIcon visual treatment

-> Modeled as a set of items around a circle
-> Modulate the radius and icon size as number of items grow
-> Clip the icons by a circular clip aligned to the background drawable

Remaining issues
-> Probably want to move to a programmaticly drawn circle + shadow
-> Anti-aliasing of the clipped region will need more attention
-> Need to animate all items in the preview as it changes (this
   wasn't required before)

Change-Id: I678ec605f6c8a34e9d7e4aec4e9583e36a9ef394
diff --git a/res/values/dimens.xml b/res/values/dimens.xml
index 468beaa..fee62dc 100644
--- a/res/values/dimens.xml
+++ b/res/values/dimens.xml
@@ -138,8 +138,8 @@
     <dimen name="quantum_panel_outer_padding">4dp</dimen>
 
 <!-- Folders -->
-    <!-- The amount that the preview contents are inset from the preview background -->
-    <dimen name="folder_preview_padding">4dp</dimen>
+    <!-- The size of the padding on the preview background drawable -->
+    <dimen name="folder_preview_padding">6dp</dimen>
 
 <!-- Sizes for managed profile badges -->
     <dimen name="profile_badge_size">24dp</dimen>