Update Tx Image To Use Satoshis

Alternative to @cbeams's pull req #56.  This updates the image to use satoshis with currently-accurate amounts which probably won't become horribly inaccurate for at least a year.  I think it also shows the implied transaction fees better than the previous image.

Image preview: <http://dtrt.org/tmp/en-transaction-propagation.svg>

@cbeams: if this new images addresses your concerns, please close your pull request.

In the absence of critical feedback, I'll merge this pull request in 24 hours (April 14th at 23:00 UTC) or after @cbeams closes his pull request---whichever comes later.