Context managed wizard _run() methods. MODEL.

MILESTONE: all _run() methods are now context managed.

Here are the _run() methods:

    core/ScoreManager.py
            def _run(self, pending_user_input=None):

    editors/Editor.py
            def _run(

    iotools/Menu.py
            def _run(

    iotools/Selector.py
            def _run(self, pending_user_input=None):

    iotools/UserInputGetter.py
            def _run(self, pending_user_input=None):

    managers/Manager.py
            def _run(self, pending_user_input=None):

    wizards/InstrumentCreationWizard.py
           def _run(self, pending_user_input=None):

    wizards/InstrumentSelectionWizard.py
           def _run(self, pending_user_input=None):

    wizards/PerformerCreationWizard.py
            def _run(self, pending_user_input=None):

    wizards/PitchClassTransformCreationWizard.py
           def _run(self, pending_user_input=None):

    wizards/ReservoirStartHelperCreationWizard.py
           def _run(self, pending_user_input=None):

    wizards/Wizard.py
           def _run(self, pending_user_input=None):

    wranglers/Wrangler.py
            def _run(self, pending_user_input=None):

MODEL: there is an idea of a "controller protocol". Controller classes
implement _run().