Show account filters in navigation drawer

- Remove the blue rectangle and use a white background of height 24dp.
- Navigation drawer design: https://docs.google.com/a/google.com/document/d/1oVptSYWa84CGt2mIQxmRObLVqopJUUilZxlARCJaiMs/edit?usp=sharing
- The external text "labels" corresponds to "groups" in code; the text
  "Accounts" corresponds to "filters" in code.
- Avoid opening AccountFilterActivity from filter header.

Bug 27687799
Bug 28245667
Fixes 28245762
Fixes 28245372

Change-Id: I75efa2fca05a1c5b74051f43e342a61f937602a1
diff --git a/res/layout/nav_header_main.xml b/res/layout/nav_header_main.xml
index cd6d559..37a33f4 100644
--- a/res/layout/nav_header_main.xml
+++ b/res/layout/nav_header_main.xml
@@ -20,7 +20,7 @@
     xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
     android:layout_height="@dimen/nav_header_height"
-    android:background="@drawable/side_nav_bar"
+    android:background="@color/contacts_accent_color"
     android:gravity="bottom"
     android:orientation="vertical"
     android:paddingBottom="@dimen/nav_activity_vertical_margin"