Epic: Refactoring of the XOAI library

[poikilotherm]

• Remove Log4J usage and any dependencies using it
• Use System.Logger SLF4J for logging
• Add docs on how to set log levels from using applications
• Switch all tests to JUnit5
• Switch all java.util time classes to java.time classes
• Try to get rid of com.lyncode.xml
• Use modern Java XML Binding and writing
• Update Hamcrest (replace?)
• Switch all packages from org.dspace to io.gdcc
• Remove Apache HTTP client and use JVM native (makes the lib JDK11+)
• Use Java 8/11 constructs like autoclosables, streams etc
• Provide interfaces used as XOAI extension points for application with default methods (e. g. for data-provider sets interfaces)
• Double-check every module for reading back data from a stream that might not contain data due to a writer buffer (this caused trouble that appeared as failing tests)

[poikilotherm]

Started in https://github.com/gdcc/xoai/tree/branch-5.0