Add option for pre-v5.1.0 custom followers behaviour

**Is your feature request related to a problem? Please describe.**
I am using this great library for my app, and before v5.1.0 (5.0.4 and below), custom followers used to move by the amount of their height. Since 5.1.0, the custom followers now move all the way until they are off the screen. (which is great for most views that are added as followers, with some exceptions)

**Describe the solution you'd like**
I've been using this library to hide my NavBar and TabBar, and above my TabBar there is an advertisement (banner) which has a height of 50. With the previous version of the library, the ad moved down, along with the TabBar and then it stayed at the bottom of the screen, where the TabBar normally is. With the new version, the ad gets hidden, out of the screen bounds, along with the TabBar. This is not the behaviour I desire. Would it be possible to add an option to the followers, to use the "new" or the "old" following method? (like the option we have for the direction of the followers)

**Describe alternatives you've considered**
For now I'm still using v5.0.4 of the library, to keep the functionality I need, but I would like to be able to use the latest features and bug fixes, as well as the Swift 4.2 version of the library.

Thank you very much for your help and your work.