Add notification when a download is completed

- fyne notication looks for the app icon to display it in the notication, so I setted the icon  in `main.go`.
- deleting points after "Download" option in grid view that I mistakenly leave it in a previous PR.
- adding the new paremeter `downloadName`

Screenshot:

Fixes #202

ui/browsing/albumpage.go

@@ -202,7 +202,13 @@ func NewAlbumPageHeader(page *AlbumPage) *AlbumPageHeader {
 						sharedutil.TracksToIDs(a.page.tracks))
 				}),
 				fyne.NewMenuItem("Download", func() {
-					a.page.contr.ShowDownloadDialog(a.page.tracks)
+					go func() {
+						album, err := a.page.mp.GetAlbum(a.albumID)
+						if err != nil {
+							log.Print("Error while getting the album: ", album)
+						}
+						a.page.contr.ShowDownloadDialog(a.page.tracks, album.Name)
+					}()
 				}))
 			pop = widget.NewPopUpMenu(menu, fyne.CurrentApp().Driver().CanvasForObject(a))
 		}

ui/browsing/playlistpage.go

@@ -262,7 +262,7 @@ func NewPlaylistPageHeader(page *PlaylistPage) *PlaylistPageHeader {
 						sharedutil.TracksToIDs(a.page.tracks))
 				}),
 				fyne.NewMenuItem("Download", func() {
-					a.page.contr.ShowDownloadDialog(a.page.tracks)
+					a.page.contr.ShowDownloadDialog(a.page.tracks, a.playlistInfo.Name)
 				}))
 			pop = widget.NewPopUpMenu(menu, fyne.CurrentApp().Driver().CanvasForObject(a))
 		}

ui/browsing/playlistspage.go

@@ -120,7 +120,7 @@ func (a *PlaylistsPage) createGridView(playlists []*mediaprovider.Playlist) {
 				log.Printf("error loading playlist: %s", err.Error())
 				return
 			}
-			a.contr.ShowDownloadDialog(pl.Tracks)
+			a.contr.ShowDownloadDialog(pl.Tracks, pl.Name)
 		}()
 	}
 }