Restructure ProtoBuf & gRPC project structure

- pom.xml {protobuf, grpc}-dependencies to consolidte
  plugin configuration, dependency version property

- {protobuf, grpc}: ONOS App to load required feature/bundle

- all other atrifacts: Apps using protobuf/grpc inherit
  ~-dependencies above to reduce copy & paste configurations and
  dependency versions.

Change-Id: Ied90aff78ffddac6228d46e85e01d035eec37bee
diff --git a/incubator/pom.xml b/incubator/pom.xml
index afd3f07..9a0702c 100644
--- a/incubator/pom.xml
+++ b/incubator/pom.xml
@@ -35,6 +35,8 @@
         <module>core</module>
         <module>net</module>
         <module>store</module>
+        <module>protobuf-dependencies</module>
+        <module>grpc-dependencies</module>
         <module>protobuf</module>
         <module>rpc</module>
         <module>rpc-grpc</module>