Move MongoDB classes into a seperate db module (#62)

* move album class into mongodb dir

* inherit AlbumMethods at DB Initialization level

* move album -> db/mongodb

* move mongodb classes into separate package

server/app/instances.py

@@ -1,14 +1,12 @@
 """
 All the MongoDB instances are created here.
 """
-from app.db import albums
-from app.db import artists
-from app.db import playlists
-from app.db import trackcolors
-from app.db import tracks
+from app.db.mongodb import albums
+from app.db.mongodb import artists
+from app.db.mongodb import playlists
+from app.db.mongodb import tracks
 
-tracks_instance = tracks.AllSongs()
+tracks_instance = tracks.Tracks()
 artist_instance = artists.Artists()
-track_color_instance = trackcolors.TrackColors()
 album_instance = albums.Albums()
 playlist_instance = playlists.Playlists()