LeCroy X-Stream oscilloscope support

libsigrok now supports the LeCroy X-Stream series of oscilloscopes (and possibly others).

This includes models from the WaveAce, WaveJet, WaveSurfer, and WaveRunner series in theory; some models may also be manufactured/rebranded by Atten, Iwatsu, or Siglent.

All these devices seem to use a common SCPI protocol and LeCroy's common waveform template format, so they should all work in theory.

Testing and/or patches fixing implementation details to support more models are highly welcome!

The code was contributed by Sven Schnelle, thanks a lot!