Integrate CXFT interface into Cheetah and implement mapping of de-dispersed time-series to Dispersion Measure value

The calls to the OpenCL and GPU FFT modules exist in Cheetah, there is currently no CPU version. This work will implement the CXFT interface of those modules.

This includes implementing mapping of de-dispersed time-series to DMs between the de-dispersion and Fourier transform components.

It also includes running a manual test of a Cheetah pipeline with an SKA1-MID test vector receptor component, with GPU-based de-dispersion and Complex Fourier transform components, using a test vector.