Create utility for unit testing of CXF REST endpoints

When developing new REST endpoints, it is currently not possible to test those endpoints using unit tests using CXF. Jersey does provide several utility classes to make it possible to quickly create and run unit tests, see [1]. As part of this effort, investigate to which extent CXF also has similar utility classes, if not create them and provide documentation for Engineering how to use them.

[1] https://jersey.java.net/documentation/latest/test-framework.html