MPS-20612 - implementation stripping for j.m.lang.plugin
per-root persistence v9 corrected (fixes MPS-20690 [build:IC-139.144] Can't load load model in plugin)
ModelReader9Handler knows about per-root persistence
fix "Couldn't read MyClass.mpsr: attribute ref is absent" and empty model as a result in v9 per-root in plugin
fix "contents"/"node" tag problem
correct import/lang indices in per-root persistence