Target Java release 11

[barend]

Building for release 8 is triggering deprecation warnings now. Moving to 11 allows a little bit of project cleanup.

• move module-info.java from src/main/java11 into src/main/java.
• delete module.info.class from src/main/resources.
• update <release> configuration for maven-compiler-plugin
• update <source> configuration for maven-javadoc-plugin
• delete profile java11-module from <profiles> section

Java 8 might still be in use in a bunch of legacy Spark 2.x code. Android and Spring-Boot have moved on.