Resolve "Feature: JavaHandler"

- add implementation for Java handler, mark Java handler as experimental in compiler
- use (prefixeded) methods "registerConsumer" and "push" in given root node (to avoid getting the handler object)
- update documentation for Java handler and some other small details
- begin with changelog for 1.0.0
- add EvaluationCounter commandline arg, counting receive/send, stages of mapping application (not directly related to JavaHandler)
- make mappings non-static, and fix tests afterwards (not directly related to JavaHandler)
- add missing fix for CI, i.e., ragdoc-view should always run (not directly related to JavaHandler)