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/mediaprovider.go

@@ -39,6 +39,8 @@ type MediaProvider interface {
 
 	GetAlbum(albumID string) (*AlbumWithTracks, error)
 
+	GetAlbumInfo(albumID string) (*AlbumInfo, error)
+
 	GetArtist(artistID string) (*ArtistWithAlbums, error)
 
 	GetArtistInfo(artistID string) (*ArtistInfo, error)

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

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 {