logitech-control-center: new version 3.9.1.b20 and more

Changes included in this pull request:
- updated to version 3.9.1.b20 (not sure if the "b" is meant to be "beta" or "build", but the version has been out for a few months now and it is supposed to address a bug with Mavericks)
- added version 3.5.1 for Snow Leopard and older
- changed homepage to URL specific to this software
- added dependency on Mavericks or older (based on lack of Yosemite info on the homepage)