This patch contains a very naive implementation of the
NSVisualEffectView. This will only work on very recent unreleased
version of Safari, but should be supported by all at some point. This
allow to use the Yosemite/iOS blurry effect.
Not all options are supported (especially the
`CPVisualEffectBlendingModeBehindWindow` mode…). But hey! it’s a start
:)
Tests in Manual/CPVisualEffectViewTest
