XamJam.Wall UWP and Droid Resize Support

[jasonCodesAway]

In case the user changes the app's window size (only possible on UWP and Droid as of now): XamJam.Wall should listen for max screen size changes in the event of a resize, this is done in the ctor, current relevant code is:

public WallView(WallViewInputs<TView, TViewModel> wallViewInputs)
{
    this.wallViewInputs = wallViewInputs;
    // TODO: Listen for screen size changes and, with thread synchronization, add support for the new maximum # of views to create
    var size = Plugin.XamJam.Screen.CrossScreen.Current.Size;
    var maxScreenWidth = size.Width;
    var maxScreenHeight = size.Height;