Allow to scope settings by platform

[arnaud-lecat]

Hi

I develop on 3 different platform. When synchronizing settings, snippets and so on, i often must change path, adjust font-size, etc...

So, it could be great if we had a per platform settings set (Windows, Mac, Unix)

[dbaeumer]

@bpasero, @aeschli FYI.

[bpasero]

#8962