Code signing release for macOS

[bhou]

Related to #61, this issue is specific for macOS

[bhou]

This would take longer than expected, as Apple's new Notarization process requires the app signs all included binaries. However, JDK8 does not compliant with the new Apple signing methods, the Notarization process complains the bundled JDK8 binaries, (built with a SDK version lower than 10.9)

Two solutions:

1. build JDK8 with xcode 10. there is a github repo doing this, but I can't make it work: see: https://github.com/stooke/jdk8u-xcode10/issues/3
2. test if it works with JDK11,
   • Flink seems supports JDK11 well
   • Spark does not support java 11 yet, will be resolved until spark3. See: https://stackoverflow.com/questions/51330840/why-apache-spark-does-not-work-with-java-10-we-get-illegal-reflective-then-java
   • Dataflow to be checked, but apache beam is on the road, see https://issues.apache.org/jira/browse/BEAM-2530

[bhou]

The JDK8 built with Xcode 10 is not stable, I met several crashes when running jobs with it. The code signing & notarization automation process is done. However, the JDK8 issue is still a blocker. Move this issue to release 0.10.0 with better tests on JDK 11 and all supported execution engines.