tests: Support standard unittest `load_tests` protocol
tests: Support standard unittest `load_tests` protocol

The same tests that are run by `./setup.py test` can now also be run
with `python -m unittest Orange.tests`.

qPCR4vir/orange3,qPCR4vir/orange3,cheral/orange3,cheral/orange3,qPCR4vir/orange3,cheral/orange3,cheral/orange3,qPCR4vir/orange3,qPCR4vir/orange3,cheral/orange3,cheral/orange3,qPCR4vir/orange3