Ability to download from grid

- Adding the option to download the album or tracks in grid view from Artist and Album pages.

ui/widgets/gridview.go

@@ -89,6 +89,7 @@ type GridViewState struct {
 	OnPlay              func(id string, shuffle bool)
 	OnAddToQueue        func(id string)
 	OnAddToPlaylist     func(id string)
+	OnDownload          func(id string)
 	OnShowItemPage      func(id string)
 	OnShowSecondaryPage func(id string)
 
@@ -217,6 +218,11 @@ func (g *GridView) createGridWrap() {
 					g.OnAddToPlaylist(card.ItemID())
 				}
 			}
+			card.OnDownload = func() {
+				if g.OnDownload != nil {
+					g.OnDownload(card.itemID)
+				}
+			}
 			return card
 		},
 		// update func