Tests: Ensure that the CDF is empty after the test case

[t-b]

• [x] Fix all tests
• [x] Nicify commits
• [x] Introduce common function for cleaning up OperationQueue's V_flag
• [x] Check all occurences of operation queue invocations and use new cleanup function
• [x] Add tests for GetListOfObjects with typeFlag in bugfix commit
• [x] WM bugreports:
  • [x] SetOperationVar issue without registered output variable: Does not reproduce in MWE
  • [x] VariableList does not complain about invalid values
  • [x] Crash when trying to morph a permanent datafolder to a free datafolder

Close #2144

[t-b]

Fixed, see the attached range diff: range-diff.txt