Add GitLab CI Configuration

See merge request hifis-technical-platform/helmholtz-marketplace-server!2

change version for Docker to 19.03.11

remove `maven-wrapper.jar` from the repository

add basic project configuration stuff

See merge request hifis-technical-platform/helmholtz-marketplace-server!1

remove `maven-wrapper.jar` because it is downloaded when building (https://github.com/takari/maven-wrapper#usage-without-binary-jar)

add Dockerfile and add configuration to respect X-Forward-* headers

add option to pass the secret for the Helmholtz AAI into the Docker container

Motivation:

The Helmholtz AAI service is a Identity and Authorisation
Management (IAM) system which arbitrates authenticated
access to registered services in the context of the Helmholtz
Assosiation. Integrating Helmholtz AAI service into the
Helmholtz Marketplace is in alignment with the goal of this
project.

Modification:

- authenticate -> able to get token
- logout
- enable csrf support

Result:

User can now be authenticate using Unity IDM.

Motivation:

A web server for helmholtz marketplace. This will be use to serve
the static files in `helmholtz-marketplace-webapp` repository.

Modification:Ã

Add boilerplate code generated by Spring Initializr.

Result:

A spring boot application that will be use to serve web related
static files and oauth2 client.