New Carousel layout and ColumnCount property

Carousel layout

The ListLayout property of the HorizontalListView has now a new value:

public enum HorizontalListViewLayout
{
    Linear = 0,
    Grid,
    Carousel,
}

The Carousel value!
Setting this, you will have a nice Carousel effect (meaning only one item is displayed at a time)

ColumnCount property

public int ColumnCount { get; set; } = 0;

You can now specify the number of column you want for the view and it will automatically compute the item width.
For this to work the ItemWidth property must be set to 0 (its default value).

Various inconsistencies fixes (and semantic changes)

Before v0.9.8, the CollectionPadding property was behaving differently on Android and iOS.
On Android, if the Thickness was equal to 0, the ItemSpacing was used as a padding.
If we wanted to have spacing between items with no collection padding, it wasn't possible.
Moreover, iOS was implementing it the right way: you could have a collection with 0 padding.