sub schema (SchemaAttributePathInstance) domain model extension + test re-factoring

* incl. new init_internal_schema.sql script (+ generation via code)
@jnauber or @chrode - may be you can clarify if we need to undo this commit not to harm the sub-module structure? Sorry, I'm still not sure about the sub-module topic. We have a commit that whants to delete "controller/src/docs/ui" in the current pull request and wonder if this may have been commited unintentionally.