tests: Added "app_class" fixture
tests: Added "app_class" fixture

see http://pytest.org/latest/unittest.html#mixing-pytest-fixtures-into-unittest-testcase-style-tests

RBE-Avionik/skylines,Harry-R/skylines,RBE-Avionik/skylines,snip/skylines,Harry-R/skylines,TobiasLohner/SkyLines,shadowoneau/skylines,skylines-project/skylines,Turbo87/skylines,shadowoneau/skylines,Turbo87/skylines,shadowoneau/skylines,skylines-project/skylines,shadowoneau/skylines,Turbo87/skylines,Harry-R/skylines,kerel-fs/skylines,RBE-Avionik/skylines,kerel-fs/skylines,skylines-project/skylines,skylines-project/skylines,TobiasLohner/SkyLines,snip/skylines,Turbo87/skylines,kerel-fs/skylines,Harry-R/skylines,snip/skylines,TobiasLohner/SkyLines,RBE-Avionik/skylines