Added r820t support.

git-svn-id: https://svn.spench.net/main/gr-baz@775 693e1593-6c1f-0410-997a-f041c8489887
Clean-up R820T code
Add gain control

git-svn-id: https://svn.spench.net/main/gr-baz@776 693e1593-6c1f-0410-997a-f041c8489887
Moved to libusbx (from libusb1)

git-svn-id: https://svn.spench.net/main/gr-baz@777 693e1593-6c1f-0410-997a-f041c8489887
libusb1 and libusbx depending on LIBUSB_FOUND
Added Compro Videomates & Cinergy rev 3

git-svn-id: https://svn.spench.net/main/gr-baz@778 693e1593-6c1f-0410-997a-f041c8489887