Settings Sync

Setting up sync is a good feature to use Flow between devices, which make our experience better.

If flowlaunchher has no plans to create an account system or buy a server, syncing through OneDrive, GoogleDrive, WebDav is also acceptable and a good solution. For example, tampermonkey, violentmonkey use these methods.

I think we can sync the settings folder, themes folder, and a list of plugins.
It's a ok to sync like `vscode`, only a json file with the list of plugins.