Eavluate support for JDK 9

[katmatt]

Just a container issue, we should split it later in smaller issues.

Topics

• Analyze problems related to our maven build and JDK 9
• Support for Java Platform Module System - without breaking our OSGi support 😉
• Support for reactive streams, review our reative streams support (see https://github.com/commercetools/commercetools-jvm-sdk-reactive-streams-add-ons)
• Add javadoc 9 full text search (which would solve Implement a full-text search for Javadoc or use some service/library #161) to our build
• Evaluate running sunrise with JDK 9

[heshamMassoud]

Just for information:

We would have a problem with the name of our module sdk-http-ahc-2_0, due to the underscore to be able to identify it as an automatic module name in JDK9, more on it here: https://stackoverflow.com/a/48714979/5654504