Similar songs (#18)

* Support for getting similarSongs from navidrome

* Ability to load topSongs from navidrome

* Load artists not in library from navidrome

src/music_service.ts

@@ -39,10 +39,12 @@ export const NO_IMAGES: Images = {
   large: undefined,
 };
 
+export type SimilarArtist = ArtistSummary & { inLibrary: boolean };
+
 export type Artist = ArtistSummary & {
   image: Images
   albums: AlbumSummary[];
-  similarArtists: ArtistSummary[]
+  similarArtists: SimilarArtist[]
 };
 
 export type AlbumSummary = {
@@ -179,4 +181,6 @@ export interface MusicLibrary {
   deletePlaylist(id: string): Promise<boolean>
   addToPlaylist(playlistId: string, trackId: string): Promise<boolean>
   removeFromPlaylist(playlistId: string, indicies: number[]): Promise<boolean>
+  similarSongs(id: string): Promise<Track[]>;
+  topSongs(artistId: string): Promise<Track[]>;
 }