Migrate fft_client and fft_server services to the open-horizon-services project

[t-fine]

With the creation of the open-horizon-services project, I think the fft services would better fit in that project.

https://github.com/open-horizon/examples/tree/master/edge/services/fft_client
https://github.com/open-horizon/examples/tree/master/edge/services/fft_server