Modify layout in Collection component.

The Collection component shows a new area for listening similar artists.
The view is only shown when an artist is selected in the artist
selection view on the left side.
Show album's year in CollectionView's section.

The CollectionModel class provides a get() function which returns a
variant map with the item at the given index. The CollectionView has a
new javascript function albumSection() which returns the first (or all)
songs for a specific album. This function is used to get the first item
of each section and fetch it's meta informations.