Optimizing mvn calls and make targets

• a separate mvn clean call should not be necessary (I left it in place for the setup target, in case this really make sense)
• mvn verify includes the compile and package phases (see Maven build lifecycle below)
• generate-spec target did point to install-yarn and validate-spec which also pointed to install-yarn

Maven build lifecycle: https://maven.apache.org/guides/introduction/introduction-to-the-lifecycle.html#a-build-lifecycle-is-made-up-of-phases