Feature/junit5

[Thadoy]

• Please check if the PR fulfills these requirements

• [ x ] The commit message describes your change

• [ x ] Tests for the changes have been added if possible (for bug fixes / features)

• [ x ] Docs have been added / updated (for bug fixes / features)

• [ x ] Changes are mentioned in the changelog (for bug fixes / features)

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

• Migrated JUnit 4 to JUnit 5

• Added a JUnit Extension instead of the JUnit Runner

• Dropped powermock, since it's no longer developed and it has no support for JUnit 5

• What is the current behavior? (You can also link to an open issue here) Uses JUnit 4

• What is the new behavior (if this is a feature change)? Uses JUnit 5

• Does this PR introduce a breaking change? (What changes might users need to make in their setup due to this PR?) The SpringDaemonTestRunner does no longer exist, test using this Runner will have to switch to JUnit 5 und use SpringDaemonExtension.

The deprecated Class SecurityContextUtilTest was deleted.

• Other information:

[YukiInu]

Please postpone this MR for a week because we need an intermediate release because of security issues with spring/cxf/jetty :/