Added maven pom.xml files.
Update gitignores
Update gitignore
Merge branch 'master' into mvn-build
Change plugin projects that do not depend on Eclipse to regular Java projects.
Skip running the tests because they require files which are not automatically built yet.
Change org.spoofax.interpreter.ui to Maven plugin parent.
Fixes for two-stage build and cleanup.
Remove versions from external dependencies and plugins, are now managed by the parent pom.