Add UI for viewing the album info returned by Subsonic getAlbumInfo API

- Adding "Get Info" in album page's "meatball" menu. When the option is clicked a pop up appears with
the album information and links to Last.fm and MusicBrainz.

Screenshot:

Fixes #105

backend/mediaprovider/model.go

@@ -18,6 +18,12 @@ type AlbumWithTracks struct {
 	Tracks []*Track
 }
 
+type AlbumInfo struct {
+	Info          string
+	LastFMUrl     string
+	MusicBrainzID string
+}
+
 type Artist struct {
 	ID         string
 	CoverArtID string