Add a script to keep the 'TrackMate-dev' update site up-to-date

This script is intended to be run by this Jenkins job:

	http://jenkins.imagej.net/view/Fiji/job/TrackMate-dev-update-site

A couple of things are left to do for the future:

- reconcile with upload-update-site.sh

- avoid the "dummy" hack by teaching MiniMaven to install artifacts from
  remote repositories (without having to make them dependencies first)

- fix the bug in MiniMaven that makes it remove miglayout-swing.jar

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
upload-update-site: restructure update-site information handling

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>