Some reworkings and refactorings

- remove obsolete methods
- rearrange methods: locate methods with similar concerns in the same area
- add JavaDoc on GitHubApi methods
- add unit test GitHubApi.getLanguages()
- ignore main / IntegrationTest.run() default wise
switch application start to java -jar mode

- java -jar target/github-api-ninja-1.0-SNAPSHOT-jar-with-dependencies.jar