Bug fix

Fixed bug when testing if can add item to sack
updated sort algorithm
ImplementedBranchAndBound algorithm
tweaking algorithm for BranchAndBound
Change KnapsackSolver to interface
tweaks
renamed to branch and bound depth first linear relaxation knapsack solver

renamed to branch and bound depth first linear relaxation knapsack
solver
also optimised knapsack to compute weight and value as items are added