Bump `cef.sdk` package to 3.2062.1876-pre1 with VS2013 specific libs too

BTW I guess we have to exercise "the split" on x86/x64 a bit on this branch with how it affects NuGet users (and prepare some communication?). We can use `CefSharp.MinimalExample` + start from scratch scenarios like the one painfully documented  in #520 for that.

Maybe we can even move `CefSharp.*` packages a bit more towards a more normal NuGet structure with `lib` folders and such? We just need to find a way to make sure we can still install both `x86` and `x64` in parallel - or should we go for a `AnyCPU` package? 

Hmm - forgive me for thinking out loud above - I hope *some* of it brings us forward though ;)
Yeah, "measure twice, cut once" and if we can find a way to get what little community CefSharp has help do *some* of the verification by kicking tires on `-pre` NuGet packages etc. I think we should be able to speed up a bit without sacrificing stability.

OK to merge this PR then?