Remove Duplicate pixels from chain during chain creation

[Jeerhz]

FIX:

• use gradient orientation table when pushing the first stack nodes of an anchor chain
• remove unused ED method pruneToLongestChain. We use the mehthod from the Chain class itself.
• use the solution that maximize F when computing the gradient using DiZenzo method for EDColor

FEAT

• Remove the method validateNode and use directly the conditions for better readability
• Remove duplicate pixels in the chain creation, no need to count for duplicated pixel stack nodes and simplify the merge of two chains.