ensure BYOE feature provides URL from which to update, and cleans up URLs when uninstalled

We recently removed 'org.eclipse.equinox.p2.touchpoint.eclipse.addRepository' touchpoints from *p2.inf files in JBDS, and the result is that until a user scans Central's update site, there are no entries listed in the Available Software Sites pref page.

So, we need to ensure that this is added back in.

Rather than putting it in the JBDS Branded Product feature, however, I would rather see it put into the BYOE / Core Features feature, so that anyone who's installed from Marketplace can also get updates from the site on devstudio.jboss.com. We can also use this mechanism to replace the 6.0-staging site (currently in Marketplace) by the 6.0 site (once we go GA) and clean the old site out of users' Eclipse installs so they only get updates from the official site, not the staging one.