enclose graph algorithms in graph namespace

alib2graph_algo/src/generate/FixedUndirectedGraph.cpp

alib2graph_algo/src/generate/FixedUndirectedGraph.hpp

alib2graph_algo/src/generate/FixedWeightedSquareGrid8.cpp

alib2graph_algo/src/generate/FixedWeightedSquareGrid8.hpp

...2graph_algo/src/generate/FixedWeightedUndirectedGraph.cpp

...2graph_algo/src/generate/FixedWeightedUndirectedGraph.hpp

alib2graph_algo/src/generate/RandomGraphFactory.hpp

alib2graph_algo/src/generate/RandomGridFactory.hpp

alib2graph_algo/src/heuristic/ChebyshevDistance.cpp

alib2graph_algo/src/heuristic/ChebyshevDistance.hpp

alib2graph_algo/src/heuristic/DiagonalDistance.cpp

alib2graph_algo/src/heuristic/DiagonalDistance.hpp

alib2graph_algo/src/heuristic/EuclideanDistance.cpp

alib2graph_algo/src/heuristic/EuclideanDistance.hpp

alib2graph_algo/src/heuristic/EuclideanDistanceNoSQRT.cpp

alib2graph_algo/src/heuristic/EuclideanDistanceNoSQRT.hpp

alib2graph_algo/src/heuristic/ManhattenDistance.cpp

alib2graph_algo/src/heuristic/ManhattenDistance.hpp

alib2graph_algo/src/maximum_flow/FordFulkerson.cpp

alib2graph_algo/src/maximum_flow/FordFulkerson.hpp