Add loaders to DrawerFragment and make status bar transparent

- This CL addresses a TODO to load groups and filters from
  DrawerFragment directly.
- Also, avoiding adding fragments to FragmentManager of a
  Fragment works around a crash on LMP.
- Wrap RecyclerView with a FrameLayout to go full screen
  with a ScrimDrawable

Bug: 34062530

Test: add and remove accounts and observe changes in side nav

Change-Id: I63943a9d596aa32301609d6ab1b9d49c0c784356
diff --git a/res/layout/nav_header_main.xml b/res/layout/nav_header_main.xml
index 518e6e6..7a2e3cb 100644
--- a/res/layout/nav_header_main.xml
+++ b/res/layout/nav_header_main.xml
@@ -16,16 +16,10 @@
   limitations under the License.
   -->
 
-<LinearLayout
+<View
     xmlns:android="http://schemas.android.com/apk/res/android"
+    android:id="@+id/nav_status_bar_spacer"
     android:layout_width="match_parent"
     android:layout_height="@dimen/nav_header_height"
     android:background="@color/contacts_accent_color"
-    android:gravity="bottom"
-    android:orientation="vertical"
-    android:paddingBottom="@dimen/activity_vertical_margin"
-    android:paddingLeft="@dimen/activity_horizontal_margin"
-    android:paddingRight="@dimen/activity_horizontal_margin"
-    android:paddingTop="@dimen/activity_vertical_margin"
-    android:theme="@style/ThemeOverlay.AppCompat.Dark">
-</LinearLayout>
+    android:importantForAccessibility="no"/>