Updated Constraints to fit all iPhone sizes

Adjusted all of the views to accommodate the multiple sizes of the
iPhones with new Storyboard layout constraints.

Also, added a ‘cell.headerImageView.contentMode =
UIViewContentMode.ScaleAspectFit’ code to auto-resize images to fit
within the confines of the UIImageViews. It may create a bunch of
“empty” space, though, depending on the aspect that is not being filled
— width or height.