windows installer: remove uninstall tracking, add welcome page
in justin's testing, the uninstall tracking was hanging the uninstall
process (on vista) for now, until we see enough need for it to warrant
more detailed testing/debugging/tweaks, I'm simply disabling the call
to confwiz --uninstall
also this adds a 'welcome page' to the install process. once the user
has installed the windows build, then the installer will open a web
browser to the 'welcome page' on the website ('/welcome_install')