Move parent pom to repository root

To support continuous integration at Travis CI, the parent pom.xml
should be located in the repository's root directory.

Instead of duplicating, move it from releng/com.es.jshint.build to
the root and adjust all project's pom files to point to this parent.
Make com.es.jshint.repository a project of its own.

Move build status icon to the top of the README.

See #66