Added a `HeadlessPlugins` plugin group, that adds more default
functionality (like logging) than the `MinimumPlugins`. Fixes#15203
Changed the headless example to use the new plugin group.
I am not entirely sure if the list of plugins is correct. Are there ones
that should be added / removed?
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The `TerminalCtrlCHandlerPlugin` has interesting effects in the headless
example: Installing it a second time it will give a log message about
skipping installation, because it is already installed. Ctrl+C will
terminate the application in that case. However, _not_ installing it the
second time (so only on the app that runs once) has the effect that the
app that runs continuously cannot be stopped using Ctrl+C.
This implies that, even though the second app did not install the Ctrl+C
handler, it did _something_ because it was keeping the one from the
first app alive.
Not sure if this is a problem or issue, or can be labeled a wierd quirk
of having multiple Apps in one executable.
55c84cc722