Change to folder structure to allow for versioning

this allows for a schema specific versions, we want to keep the schema files of older versions, to make them still loadable. This required also changes in schema_util and the tests. This also adds some basic test data to check if validation works. These test data should be full and the test fail, if the schema is changed in way which breaks the validation. Then a new version should be made instead. Related to #39 (closed) and #40 (closed).