Modify headline margins to UX spec

If both modify share and include text are present, ensure 16dp of space
between them. Ensure 16dp of space beneath the headline UI in general.

Bug: 281541996
Test: View UI with modify share or include text or both and compare
      margins to mocks.
Change-Id: Id2c1521d3a039806080c32f7e773ebc03bda7b3d
1 file changed