tests/testdata: fix naming of some testdata
tests/testdata: fix json syntax errors
tests/testdata: fix @type
validator: return all error messages as generator
schema: rename to match object type
schema: fix json syntax
schema: fix indentation
schema: load schema form seperate files

The schema is now loaded form the single files in the schema directory.
The combined file is now removed.
schema: load schema files on demand

OPARL is now a LazyDict that loads the schema definitions on demand.
This enables test to import this file even if the schema definions
are invalid json.
tests: validate schema files with META_SCHEMA
validator: validate_custom now accepts a schema

validate_custom now expectes the schema directly and does not get it
with the obj_type. This makes it easier for testing.