created package graphs/io
moved GraphReader to io 
changed AbstractListGraph : added setSize
changed Graph : added setSize
created empty contructors in LinkedGraph, ReversibleGraph,
	ContractionGraph, SearchGraph
added MultipleGraphReader
changed TestRandomContraction to use MultipleGraphReader
changed TestDepthFirstSearch to use GraphReader
added interfaces GraphFiller, SizeCounter
added AbstractSizeCounter
implemented SimpleSizeCounter, SimpleGraphFiller, SearchGraphFiller,
SearchSizeCounter
deleted ContractionGraphReader, AbstractSearchGraphReader,
SearchGraphReader, SimpleGraphWriter