Use Tango cmake config file if available
Tango 10 installs a cmake config file now, we should use this if it is found, rather than our scripts.
This will probably also resolve #5 (closed), but note that currently (10.0.0-rc1) we do not install the cmake config file on Windows (cppTango#1277 (closed)), which means we might need to handle the dependencies ourselves on Windows.