Auto-detect whether OPC-UA support is present and use it if possible

[gavanderhoorn]

Recent Fanuc controllers/system software versions could have OPC-UA support.

As much of the functionality in dominh could be implemented using that, it would be good for dominh to try and use it when possible.

But as dominh should remain usable with controllers/system software versions which do not have OPC-UA, it should remain optional.