Replace C-style casts

C-style casts are extensively used in the older sections of code, for example, in AtomicConvolver.cpp:

_realData = (double*)fftw_malloc(nrows * ncols * sizeof(double));
_transformedData = (fftw_complex*)fftw_malloc(nrows * _halfCols * sizeof(fftw_complex));

These should be replaced with C++ casts, specifically static_cast.