Refactored protobuf framework, added loader

Included changes:

* Initial adapter interface spec
* Adapter loader to auto-load adapters
* Initial adapter NBI
* Better import support in chameleon, allowing more flexible
  protobuf structure (by organizing artifacts and service
  into separate proto files.
* Refactored voltha.proto to split things into logical proto
  modules.
* Some additional cleanup

Change-Id: I75f9883c6992148ea8df430bcdaebf85115fea4a
diff --git a/.gitignore b/.gitignore
index 156a805..2b3e6ef 100644
--- a/.gitignore
+++ b/.gitignore
@@ -31,8 +31,8 @@
 *.swp
 
 # Protobuf output files
-#voltha/**/*.desc
-#voltha/**/*_pb2.py
+voltha/**/*.desc
+ofagent/protos/**/*_pb2.py
 
 # Editors
 *.bak