Made changes as per the comments on patch set 2.
Made changes as per comments on patch set 3.
Made further changes and event subscription works absolutely fine now.
Change-Id: Icd20195f6c0e045d14beb73584069d486ab9290c
1. Refactored the application into two java projects api and app as per convention
2. Deleted the onos-app-gpb project. The proto files are consolidated in the
incubator-protobuf project as per suggestions.
3. Some code to translate ONOS Event pojo messages to GPB format.
4. Implementation of Subscribe and Unsubscribe APIs.
5. Minor changes due to review comments from 9212 and 9053
6. Refactored the proto fileso that its a 1:1 mapping between the core type to proto message.
Change-Id: I2bcc0de96150f838ccfe9e49293fe61d94062628