Fix UX of automated updates
When I open Musescore it finds new updates and asks me if I want to install them. This is good.
But if I close Musescore while it downloads then it doesn't update and when I next open Musescore it redownloads the installer.
If I don't close Musescore before the setup starts then the setup fails and when I next open Musescore it redownloads the installer.
1) Close Musescore automatically when the setup phase begins (this is most important change)
2) Save the installer to one consistent folder and reuse it if it exists rather than redownloading it every time