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/subsonic/subsonicmediaprovider.go

@@ -59,6 +59,19 @@ func (s *subsonicMediaProvider) GetAlbum(albumID string) (*mediaprovider.AlbumWi
 	return album, nil
 }
 
+func (s *subsonicMediaProvider) GetAlbumInfo(albumID string) (*mediaprovider.AlbumInfo, error) {
+	al, err := s.client.GetAlbumInfo(albumID)
+	if err != nil {
+		return nil, err
+	}
+	album := &mediaprovider.AlbumInfo{
+		Info:          al.Notes,
+		LastFMUrl:     al.LastFmUrl,
+		MusicBrainzID: al.MusicBrainzID,
+	}
+	return album, nil
+}
+
 func (s *subsonicMediaProvider) GetArtist(artistID string) (*mediaprovider.ArtistWithAlbums, error) {
 	ar, err := s.client.GetArtist(artistID)
 	if err != nil {