Added 'gen-py/' to .gitignore
Regenerated Thrift code using latest Concrete schema
Replaced copy_thrift_generated_classes.sh with generate_thrift_classes.sh

Updated build script for package maintainers now that the .thrift
definition files have been moved from the 'concrete' repo to the
separate 'concrete-thrift' repo.
Updated README with info about new concrete-thrift repo
Added __str__() to UUID class
Added test file produced by Concrete-Agiga pipeline
Updated validation code to use classes for UUIDs instead of strings

The Concrete (Thrift) schema has changed, so that UUID's are now
stored as instances of the UUID class instead of as strings.