setup: licence statement fix

* Fixes licence classifier in `setup.py` that mistakenly read MIT
  instead of GPLv2+.

* Fixes licence statement in `tox.ini`.

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
setup: PEP 8 improvements

* Amends long line in the Python classifier list, making TravisCI PEP 8
  tests pass again.

* Amends import order to conform more fully to PEP 8 recommendations.

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>