Insert new header comment block, remove old one, manually improve file comments (defines / implements), change brief function description to doxygen format, remove some outcommented code

Complex integrator implemented; standard integrator now reuses integration workspace, FormFactorSphere refactored

Fixed bug in InterferenceFunction2DParaCrystal; fixed warnings about size_t -> int conversions; updated Xcode project file

Fixed issues with complex Bessel function in cylinder form factor + corrected normalization of Gaussian and Lorentzian form factors

Evaluate form factors for complex wave vectors (1): provide interface and implemented it for part of the Formfactors