Deploy releases directly to maven central on the new Sonatype infrastructure..

To reduce risk of a release getting stuck in an intermediate state on bintray, make all official releases to maven central.

Resolves #1180.

ci/Dockerfile

@@ -1,6 +1,6 @@
 FROM adoptopenjdk/openjdk8:latest
 
-RUN apt-get update && apt-get install -y jq
+RUN apt-get update && apt-get install -y jq gpg
 
 RUN apt-get clean \
  && rm -rf /var/lib/apt/lists/*