Common actions allow for shortcuts to be registered for actions
which do not yet exist, or which are not associated with a single
global QAction object attached to at the application level. For
example, code editor actions which will be created as children
of individual code editor widgets, but which should have
shortcuts available for user configuration via the shortcuts
manager dialog.
For the c++ api dox this expands to "\c nullptr" (the
\c directive indicates a code literal value), and for sipify/Python
it expands to ``None`` (`` is sphinx annotation for literal values)
Makes for nicer dox for both c++ and Python!
