Update/Fix a few elements to validate GivensFGFTParallel C++ impl.

- Fix the deletion of pivot candidates in GivensFGFTParallel: when pivot (p,q) is selected, all pivot candidates (p',q') such that p'==p or q'==p or p'==q or q'==q must be deleted from candidates (as in the matlab script).
- Change the matlab ref. script and the C++ impl. to store all pivots (only the last one was kept).
- Change the Laplacian matrix again in test data mat file (return to the same used for GivensFGFT parent algorithm), store the good pivots (since we store all of them now).
- Update output for pivots in test GivensFGFTParallel.cpp.in.