Skins: store the default skin on client only

I'd like to use the light skin on my desktop and the dark skin on my mobile phone. Maybe we should add a way to either

1. store this setting only in localStorage
2. allow the user to say that it wants to store it locally only and not on the server. This would allow to still have the light skin instead of the default on all new devices but on one device (its mobile phone) have the dark skin.

@all What do you think?