Removed a bug that was implemented when improving the summation

Also included a more accurate summation in the fermionic contribution (Changed the result only to the order of 10^-15)

now the results are exact the same

Still, the improven summation results in roughly a factor six faster computation of the fermionic contribution

Next step is to implement a specialisation for L^3 x 2*L
Added a speciallization for the computation of the fermionic contribution on L^3 x 2L lattices. Gained a factor of approx 5
Added an improved summation of the propagatorsums for the case of a L^4 lattice when lowMem is active.
The inrease on a pure lambda-scan was a factor 50...100 :)

Now lowMem is faster then with storing the momenta.

Next step is to add a improvement for L^3x2L an lowMem
Splitted effectivePotential.cc

Propagatorsums and fermionicContributions got their own file
Played around. Added a file to describe the improved summation