Adjust homepage styles and layouts

- Fine tune the header text size and position
- Fix the header overlapping problem on the homepage and collapsing
  toolbar pages when configuration changes by adding android:id.
- New AppBarScrollingViewBehavior for the homepage to avoid manually
  offsetting the IA
- Correct the formula of counting search box height

Test: robotest, manual
Fixes: 177967923
Fixes: 177968564
Change-Id: Id3ed44f4296fa2a19d6890b009d3881a5c140bbd