Show scene properties and variables in the side panel

[D8H]

https://gdevelop-storybook.s3.amazonaws.com/scene-side-panel/latest/index.html?path=/story/layouteditor-compactscenepropertieseditor--default

[4ian]

Looks good to me! This being said, I realized that there is no variable refactoring for scene variables and object variables in this properties panel.

I think it's important to do it now (we can discuss how to do it properly) as it's important to be able to rename a variable and have the events continue to work (it works for the variable dialogs, so it's a bit weird it's not working in the properties panel).
Because the properties panel is much more "realtime" change, we will probably have to launch the refactoring after any change/blurring of a variable name. Same for objects.
Addition/deletion of a variable will probably not run anything, like now.