Investigate differences between plugins ran from the Creator and the Menu

Some properties/items seem to only work well if the plugin is ran from the menu instead of the creator. This is likely due to a difference in instantiation, see thread and comment https://musescore.org/en/node/96506#comment-428621
One of the plugins I'm working on has the opposite effect of running correctly when ran from the Creator, but failing due to different behavior when ran from the Menu (https://github.com/jeetee/MuseScore_Parsons_Code_Exporter)

Similarly I've also discovered possible cleanup issues with plugins and close-signal capturing https://musescore.org/nl/node/94801