tableau.svg: split ticket top and bottom

tableau.svg: split ticket top and bottom

Eventually we have two problems to solve:

  1. The ticket separator becomes misaligned when you scale the
     ticket background independently
  2. Only the bottom of the ticket is resized when the QR gains
     focus.

Both of these will be easier if we split the bottom part of the ticket
from the top (separator, dimples, and the stuff above them). This
commit does that. The top/bottom parts aren't grouped because we
probably won't need to manipulate them as groups, so for now, there
are just two ticket background layers with an epsilon of overlap.