Adds support to upload and download maven packages from/to GitLab

dzaporozhets:~/Projects/mvn-example master 
→ mvn deploy
...
[INFO] --- maven-install-plugin:2.4:install (default-install) @ my-app ---
[INFO] Installing /Users/dzaporozhets/Projects/mvn-example/target/my-app-1.1-SNAPSHOT.jar to /Users/dzaporozhets/.m2/repository/com/mycompany/app/my-app/1.1-SNAPSHOT/my-app-1.1-SNAPSHOT.jar
[INFO] Installing /Users/dzaporozhets/Projects/mvn-example/pom.xml to /Users/dzaporozhets/.m2/repository/com/mycompany/app/my-app/1.1-SNAPSHOT/my-app-1.1-SNAPSHOT.pom
[INFO] 
[INFO] --- maven-deploy-plugin:2.7:deploy (default-deploy) @ my-app ---
Downloading from gitlab-maven: http://localhost:3001/api/v4/projects/1/packages/maven/com/mycompany/app/my-app/1.1-SNAPSHOT/maven-metadata.xml
Downloaded from gitlab-maven: http://localhost:3001/api/v4/projects/1/packages/maven/com/mycompany/app/my-app/1.1-SNAPSHOT/maven-metadata.xml (767 B at 118 B/s)
Uploading to gitlab-maven: http://localhost:3001/api/v4/projects/1/packages/maven/com/mycompany/app/my-app/1.1-SNAPSHOT/my-app-1.1-20180806.161455-3.jar
Uploaded to gitlab-maven: http://localhost:3001/api/v4/projects/1/packages/maven/com/mycompany/app/my-app/1.1-SNAPSHOT/my-app-1.1-20180806.161455-3.jar (2.6 kB at 3.3 kB/s)
Uploading to gitlab-maven: http://localhost:3001/api/v4/projects/1/packages/maven/com/mycompany/app/my-app/1.1-SNAPSHOT/my-app-1.1-20180806.161455-3.pom
Uploaded to gitlab-maven: http://localhost:3001/api/v4/projects/1/packages/maven/com/mycompany/app/my-app/1.1-SNAPSHOT/my-app-1.1-20180806.161455-3.pom (2.0 kB at 3.1 kB/s)
Downloading from gitlab-maven: http://localhost:3001/api/v4/projects/1/packages/maven/com/mycompany/app/my-app/maven-metadata.xml
Downloaded from gitlab-maven: http://localhost:3001/api/v4/projects/1/packages/maven/com/mycompany/app/my-app/maven-metadata.xml (319 B at 809 B/s)
Uploading to gitlab-maven: http://localhost:3001/api/v4/projects/1/packages/maven/com/mycompany/app/my-app/1.1-SNAPSHOT/maven-metadata.xml
Uploaded to gitlab-maven: http://localhost:3001/api/v4/projects/1/packages/maven/com/mycompany/app/my-app/1.1-SNAPSHOT/maven-metadata.xml (767 B at 1.1 kB/s)
Uploading to gitlab-maven: http://localhost:3001/api/v4/projects/1/packages/maven/com/mycompany/app/my-app/maven-metadata.xml
Uploaded to gitlab-maven: http://localhost:3001/api/v4/projects/1/packages/maven/com/mycompany/app/my-app/maven-metadata.xml (319 B at 50 B/s)
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 17.331 s
[INFO] Finished at: 2018-08-06T19:15:04+03:00
[INFO] Final Memory: 16M/55M
[INFO] ------------------------------------------------------------------------