Verify calculation of the tchebycheff norm

[fcampelo]

Tchebycheff norm is defined as the maximum absolute value of a vector

http://mathworld.wolfram.com/L-Infinity-Norm.html http://webber.physik.uni-freiburg.de/~hon/vorlss02/Literatur/StatistikGlossar/node29.html https://en.wikipedia.org/wiki/Uniform_norm

Check whether internal calculations are using absolute values or signed values. This shouldn't be a problem (as the arguments of the norm should always be non negative for the MOEA/D), but it is important to keep these things straight.