Some source bits are stored internally at Kitware and we lack (source)
redistribution rights for them, so add an option which, by default,
hides genericio, acusolve, vistrails, and their dependents from the
superbuild to avoid confusion by people who don't have access to them.

Change-Id: Ie91a825c2bda811b1df826342dc22f91c211d17b