Now you can add both subview1, 2, and barcell2 into BarCell2.

One issue, I was unable to debug. The Xamarin debugger crashes right after I click on one of the add buttons in BarCell2. However, I was able to continue the testing without the debugger in IOS Simulator.

Re-cap:
FirstView is replaced by SecondView
BarCell is replaced with BarCell2
I didn't want to touch the existing files, that's why I just excluded them from the project.

Problems
 1. Can we associate some CollectionViewCell with the CollectionView's binding WITHOUT creating a ViewModel?
    - For example, in SecondView, instead of adding BarCell2 into MainCollectionView's sub view, I'd rather first, create BarViewModel and BarCell2, then create BaseViewCell (which is of type MvxCollectionViewCell), add BarCell2 into BarViewCell (through whatever means), and then finally add BaseViewCell into MainCollectionView.
 1. How do we add a UIView into MvxCollectionViewCell through code?
 1. UI Docking