Randomized Maximal Bipartite Matching algorithm
BipartiteGraphInputFormat with example, debugged Writables

Tested with:

    run=$RANDOM
    graph=bipartitegraph-1
    hadoop fs -mkdir $graph
    hadoop fs -put src/main/java/org/apache/giraph/debugger/examples/bipartitematching/$graph.* $graph/
    hadoop jar  target/giraph-debugger-*-jar-with-dependencies.jar org.apache.giraph.GiraphRunner \
        org.apache.giraph.debugger.examples.bipartitematching.RandomizedMaximalMatchingComputation \
        -vif org.apache.giraph.debugger.examples.bipartitematching.BipartiteGraphInputFormat \
        -vip $graph
        -vof org.apache.giraph.io.formats.IdWithValueTextOutputFormat \
        -op $graph.output.$run \
        -w 1 -ca giraph.SplitMasterWorker=false
    hadoop fs -cat $graph.output.$run/part-*
minor fix to use getters
Fixed null issues with Writables
Two bug fixes in RandomizedMaximalMatchingComputation
Separated Message, VertexValue and prepared corrected versions in advance