Fix: Quit OpenTodoList before uninstalling
requested to merge 445-3-34-0-fails-to-install-on-windows-10-when-opentodolist-is-running into stable
This fixes the installer on Windows: It will close the app when it is running before running the uninstaller. This ensures that the installation runs through (otherwise, the installer will block and wait for the file to get writable again).
Closes #445 (closed)