Set upper limit for the spatial frequency of roughness

Upper-limited spatial frequency means that the spatial lateral size of relief is lower-limited.

Default spatial frequency limit 0.5 nm^-1 corresponds to spatial period 2 nm, or the homogeneity size 1 nm.

With such a limit, an rms roughness is not equal to sigma parameter of K-correlation model anymore. That is why these concepts were separated.

Real-space correlation function was removed from the code. It is not used directly in computations and with the cutoff in the reciprocal space it does not correspond to the spectrum anymore.

Reference data were updated.

Resolves #1024 (closed)