UITraitCollection support

[piercifani]

When writing layout code, you should rely on the view/viewController's traitCollection instead of just the frame of the view.

However, when executing the snapshot tests for a device, the traitCollection during the test execution is the same as the current simulator, which is not ideal when using expect(view).toMatchSnapshot(for: .allDevices) since an invalid collection is passed here.

We should either notify this in the documentation or (preferably) override the traitCollection of the UIView using override trait collection

[skyweb07]

hey sorry for not answering before, I've been a little off, I'm checking now into making a better version but I don't understand the issue, could you provide more information or maybe opening a PR?

Thanks!!