Allows user to modify scale transforms

Same pull request as [this one](https://github.com/callumboddy/CBZSplashView/pull/18) but cleaner.

It allows user to modify the scale tranforms, which was usefull for me.

I remove the Pod folder and indicate in the podspec to use the `Classes` folder (Pod folder was a duplicate of Classes). Feel free to tell me if I was doing wrong :), but from my point of view this was a mistake that could lead to problems.