Port Fourier transform of the interaction matrix (D-matrix) to GPU

[myurkin]

Is your feature request related to a problem? Please describe.

Right now the Fourier transform of the D-matrix is done with the FFTW even in OpenCL mode. This brings redundant library dependence and slightly affects performance.

Describe the solution you'd like

In OpenCL mode all Fourier transforms should be made with the clFFT. This package is mature enough.

Additional context

The performance impact is minor since this transform takes place only once. So this is low-priority issue.