Added SubDirectDecomposition

and some usefull methods :
    getConcept method
    arrowClosedA method
    arrowClosedO method
Make Java6 compliant
Correct 2 last errors generated by Java6
Yet another issue with Java6
Introduce HybridGenerators

add joinClosure, meetClosure, fullClosure and hybridGenerators methods to lattice class.
Make code Java6 compliant
Update Names : arrowClosedObject, arrowClosedAttribute
Merge pull request #114 from JeanFrancoisViaud/master

Merging for the moment. May be, we need to refactor the library to use iterators.