Split spotifyvis code into different apps (#47)

Server is able to start, but none of the apps are linked together yet.

graphs/urls.py

@@ -0,0 +1,12 @@
+from django.urls import path, include
+
+from .views import *
+
+urlpatterns = [
+    path('artists/<str:user_secret>', artist_data, 
+        name='display_artist_graph'),
+    path('genre/<str:user_secret>', display_genre_graph,
+        name='display_genre_graph'),
+    path('audio_features/<str:user_secret>', audio_features,
+        name='display_audio_features'),
+]