Tune Dashboard layouts following UX spec - part 2

- set a fixed size for the Dashboard icons (and thus fix the
Account type icons size isssue)
- tune layout for N7 tablet

See bug: #15384992 Setting Dashboard - padding updates

Change-Id: I0306f1ec2309e859e044e8490cef468def8d38fb
diff --git a/res/layout/dashboard_tile.xml b/res/layout/dashboard_tile.xml
index 8d65666..80c3a26 100644
--- a/res/layout/dashboard_tile.xml
+++ b/res/layout/dashboard_tile.xml
@@ -23,8 +23,8 @@
 
     <ImageView
             android:id="@+id/icon"
-            android:layout_width="wrap_content"
-            android:layout_height="wrap_content"
+            android:layout_width="@dimen/dashboard_tile_image_size"
+            android:layout_height="@dimen/dashboard_tile_image_size"
             android:scaleType="centerInside"
             android:layout_marginStart="@dimen/dashboard_tile_image_margin_start"
             android:layout_marginEnd="@dimen/dashboard_tile_image_margin_end"