type information in Graph and in getUndirected method
typeinfo in reverse and getOutdegrees
add dependency to flink-test-utils
test for undirected, reverse and outDegrees
remove unused imports
made functions for getUndirected, outDegrees and reverse static inner
test mapVertices
remove unecessary type from mapVertices
fixed subGraph() and added test
add tests in readme
Merge pull request #2 from project-flink/vasia-graphDSL

Changes functions to static inner classes and adds initial tests