First attempt at supporting builds with Java 11

Includes:
- Bump protobuf to 3.8.0 and grpc-java to 1.21.0 (along with transitive
  dependencies such as Netty)
- Add jaxb_api at compile time when needed (removed in JDK 11)
- Bump Bnd to 4.1 (adds support for Java 11)

To build with JDK 11, uncomment lines in .bazelrc.
Tested with Bazel 0.26.0.

Change-Id: Ib8e0c7310eacf97328762606e57c01e4834e5565
diff --git a/protocols/grpc/api/BUILD b/protocols/grpc/api/BUILD
index 5a2b2d7..3247fcd 100644
--- a/protocols/grpc/api/BUILD
+++ b/protocols/grpc/api/BUILD
@@ -1,3 +1,3 @@
 osgi_jar(
-    deps = CORE_DEPS + ["//lib:io_grpc_grpc_core_context"],
+    deps = CORE_DEPS + ["//lib:io_grpc_grpc_api_context"],
 )