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/.bazelrc b/.bazelrc
index 3bd8166..64f85c8 100644
--- a/.bazelrc
+++ b/.bazelrc
@@ -1,3 +1,10 @@
+# Build options to use JDK 11
+# build --incompatible_use_jdk11_as_host_javabase
+# build --javabase=@bazel_tools//tools/jdk:remote_jdk11
+# build --host_javabase=@bazel_tools//tools/jdk:remote_jdk11
+# build --host_java_toolchain=@bazel_tools//tools/jdk:toolchain_vanilla
+# build --java_toolchain=@bazel_tools//tools/jdk:toolchain_vanilla
+
 build --nouse_ijars
 build --experimental_strict_action_env
 test --test_summary=terse