run: Implement multi-scene scenarios

Implement support for having multiple "Scenes" in a "Scenario", in kpet.run, each "Scene" corresponding to a single run of all tests in the database against a particular kernel with a particular set of test-selection parameters.

Remove "View" and "TestView" from kpet.data, and replace them with functions extracting a list of tests from both "Scene" and "Scenario" for use in "kpet test list" and "kpet run test list".