[feature] manage multiple themes

[MobiliteDev]

Hi,

Thank you for your project, it is very great! Is it possible to imagine a way to manage theme ?

Like uploading a json config file, editing it, exporting it ...

Because I've created a great theme with your tool, but, I want now to change some things, and see in direct changes on your webSite, it is impossible, I have to set all preferences one more time, and re-export it.