* fix#11958 [BUG] python generates wrong model name and model file name
Modify AbstractPythonCodegen.toModelName just like AbstractJavaCodegen.toModelName
* add unit test
* update samples and docs
by
./bin/generate-samples.sh
./bin/utils/export_docs_generators.sh
* fix AbstractPythonCodegen#toModelName logic, remove underscore
* update samples and docs
by
./bin/generate-samples.sh
./bin/utils/export_docs_generators.sh