* #201 initial support for v3 -> v4 api changes.

* Introduce Docker for testing

* Switch to Maven in travis because releases are built with Maven anyway
* Introduce Maven-Wrapper to fixate the used Maven version.
* Reuse existing GitlabAPITest as integration test which will be run
  always when docker is available.
* Use docker-maven-plugin for starting/stopping GitLab.
* For use with Maven run `mvn -Pdocker-gitlab clean verify`. Starting
  GitLab takes a long time (>100 seconds on my Macbook Pro).
* For use in the IDE run:

```
mvn -Pdocker-gitlab,docker-ide docker:start
mvn -Pdocker-gitlab,docker-ide docker:stop
```

* Extract APIForIntegrationTestingHolder

* username/password sessions per time unit are limited

* Need at least source and target 1.7

AssertionError in Tests is only available for >= JDK7

* Use GitlabUploadIT as another integration test

* Don't choke when dockerized SUT is not available

Need to throw AssumptionViolatedException in BeforeClass because
otherwise the class is not initialized correctly.

* Add CONTRIBUTING.md and travis badge.

* Fix API calls for user block/unblock, add some calls

* block/unblock uses POST instead of PUT.
* Add ability to refine permissions for branch protection.
* Add ability to add deploy key with push permission.

* Fix getRawFileContent and getRepositoryTree