Support ViewGroup as sticky

[yanzhenjie]

The code has been submitted to #4 , such as:

<android.support.design.widget.TabLayout
      android:id="@+id/layout_tab_middle"
      style="@style/WrapContent.WidthMatchParent"
      android:background="@color/white"
      android:tag="sticky"/>

[micrologic]

If ViewPager contain fragment is not show content
<android.support.v4.view.ViewPager android:id="@+id/view_pager" android:layout_width="match_parent" android:layout_height="wrap_content"/>