Weighting fields/potential in periodic geometries

Add option to set the number of periodic copies of the basic cell to be used for calculating the weighting potential and weighting field in ComponentAnalyticField. The implementation follows the "FOURIER" instruction in Fortran Garfield (https://garfield.web.cern.ch/help/garfield_120.html#Ref0967). The CERNLIB CFFT routine was also ported for this purpose.

The default is 1 copy (as was the case up to now). The results obtained for the weighting potentials and fields when including more than 1 copy still need to be validated/benchmarked.

If the number of copies is set to zero the same functions as for the electric field and potential are used (i. e. the weighting fields and potentials have the same periodicity).