new maven jar called flatbuffers-java-grpc which contains utility … (#4558)

* new maven jar called flatbuffers-java-grpc which contains utility class supporting generated code for grpc over flatbuffers; grpc java unit test based on maven and junit (maven is used only for simplicity of testing); removed straneous namespace_test/NamespaceA/TableInC.java which is not longer used in the test and no longer generated but contains complilation errors if java compiler picks it up

* moved java grpc tests files according to review request

* Added missing generated code for Java gRPC.

Change-Id: Iada090fe2e99b80a4b7c2f8e39c838a992a1feae

* added missing name and url