Update action bar style in app header UI.

- Update background color of actionbar
- Remove elevation of actionbar so it appears to be the same entity as
  app header.
- Add a shadow below app header view. We can't set elevation on app
  header unfortunately because that will add shadow all round the view,
  but we only want shadow below it.
- Updated app icon size/text size per to match UI spec.

Change-Id: I63d7fa42b859a008fa662aaf19848cd40529c2ff
Fix: 37207527
Fix: 37079248
Test: visual && make RunSettingsRoboTests

res/values/dimens.xml

@@ -22,6 +22,7 @@
     <dimen name="action_bar_switch_padding">16dip</dimen>
 
     <dimen name="app_icon_size">40dip</dimen>
+    <dimen name="min_tap_target_size">48dp</dimen>
     <dimen name="screen_margin_sides">64dip</dimen>
     <dimen name="screen_margin_top">72dip</dimen>
     <dimen name="screen_margin_bottom">48dip</dimen>

res/values/styles.xml

@@ -416,7 +416,7 @@
     <style name="TextAppearance.EntityHeaderTitle"
            parent="@android:style/TextAppearance.Material.Subhead">
         <item name="android:textColor">?android:attr/textColorPrimary</item>
-        <item name="android:textSize">24sp</item>
+        <item name="android:textSize">16sp</item>
     </style>
 
     <style name="AppActionPrimaryButton" parent="android:Widget.Material.Button.Colored"/>