Update build - Githubissues

This PR changes all dependencies to their latest versions and fixes any inconsistencies introduced.

RADAR-Schemas is updated with the latest schemas, which affects quite some code
RADAR-Commons is updated, not much is changed
Swagger is updated. It now outputs OpenAPI 3.0 on /radar/api/openapi.json and /radar/api/openapi.yaml.
Tests are updated to use JUnit @Rule for initialising and tearing down API clients.
Unused dependencies are removed
Dependencies are moved to their proper configuration (runtimeOnly, compile, etc.)
Gradle is updated to version 4.4, and Gradle files are split by function into the gradle/ directory to improve readability.
Checkstyle definitions are updated to Checkstyle version 8.4, the version that Codacy now also uses.
Docker build uses a multi-stage build ready for production.

RADAR-base / RADAR-RestApi