Performance fixes on NetworkProjections + stopping conditions added for MDS and VQ

NetworkProjections performance improved with respect to data passing
(using member variables instead of passing arguments), stopping
conditions added to MDS and VQ to prevent unnecessary executing if
distortion/stress unchanged. Can epsilon and number of iterations
without change be modified in the code.
Merge pull request #6 from tfranovic/master

Performance fixes on NetworkProjections + MDS/VQ stopping conditions