added polygonal chamber from pyecloud

modified for taking in input a dictionary and tested with
the existing PICs, as expected results from FD (taking into accout
the chamber) are different from the others
tested dst vs FD, there seems to be a scle factor
found a Dh dependence

now the factor is grid size independent
spotted another factor pi**2

the remainig factor seems to be dependent on the size of the cavity
try to work a bit more on coeff, but i guss i'll go back
Revert "try to work a bit more on coeff, but i guss i'll go back"

This reverts commit cbf6dad3590e473781c162312d4ecbd169e46c31.
using green matrix instead of double loop.

result is unchanged
rectangular chamber seems to work

factors still to be investigated
introduced normalization factor in the dst

got rid od the other factors
it workks :-) but still in script form
created dst2 function

much cleaner now
class complete but buggy

phi is there, E field not working
the new class (FFT_PEC_Boundary_SquareGrid.py) is working
Xmas
added png to gitignore
Added comparison to christmas tree