Earl Grey swizzling fails when proxy objects are used.

I've seen this issue with projects using [TrustKit](https://github.com/datatheorem/TrustKit) and [Detox](https://github.com/wix/detox), but this is a general problem of Earl Grey.

Fox example, in NSURLSession+GREYAdditions.m, `greyswizzled_dataTaskWithRequest:completionHandler:`, the code checks if `[delegate respondsToSelector:originalSel]`, but later, `class_getInstanceMethod` returns `NULL` because the `delegate` instance is actually a proxy which implements `respondsToSelector:` and `forwardingTargetForSelector:`.

I will submit a PR with a special case fix for the case above, but consider refactoring any swizzling mechanisms taking into account `forwardingTargetForSelector:` at the very least.