Reduce SessionModel

See merge request !555

extend check for data=0 to more tests

See merge request !559

abbreviate test if data set is empty, and report accordingly

See merge request !558

improve test log

See merge request !557

Environment variable BA_NTHREADS provides default number of threads

See merge request !556

Require CMake 3.15 to ensure policy 0094

See merge request !554

Remove session signaling in sample model

See merge request !553