tableau.svg: add the MARC Train origin/destination

tableau.svg: add the MARC Train origin/destination

This (finally?) had to be hacked into the XML by hand because inkscape
isn't smart enough to handle multiple <tspan>s within a single <text>
element. We want to keep the origin, arrow, and destination all as
separate tspans (with ids) so that we can change the origin and
destination easily from a script.

Since I was already hacking it by hand, I cleaned up the XML a bit.
Hopefully it can survive a round trip through inkscape in the future.