CollectionView: SelectionMode with Navigation and LongPress

Let's use a long press gesture to initiate the multiple selection mode in CollectionView, and then a tap gesture for navigating to other pages when selection mode is none. This video continues the journey of building out a photo gallery experience in Xappy.

Resources:

• Docs: Selection
• Docs: Navigation and passing data
• Xamarin Community Toolkit: TouchEffect
• Blog: Touch Effect