Kithe

I tried to download .pak(unreal pak) file and store it to user's storage by using `DownloadFileToStorage` function. But most of the time when it downloaded ~40-80%, the download failed. And...

I've tried to config **canvas's background color** but in current project, it doesn't has `backgroundColor` params. So I made this pull request to add `backgroundColor` params to `Editor.vue` 🙂