Refactor audio feat graph

Fixes #51. Instead of passing in an array of hard coded values as the
interval end points, an object specifying the beginning, the end, and
the step size is used. Categories can be more easily defined and
modified this way.

api/utils.py

@@ -170,7 +170,7 @@ def add_artist_genres(headers, artist_objs):
     params = {'ids': artist_ids}
     artists_response = requests.get('https://api.spotify.com/v1/artists/',
             headers=headers, 
-            params={'ids': artist_ids},
+            params=params,
             ).json()['artists']
     for i in range(len(artist_objs)):
         if len(artists_response[i]['genres']) == 0:

api/views.py

@@ -166,8 +166,9 @@ def get_audio_feature_data(request, audio_feature, user_secret):
 
 #  get_genre_data {{{ # 
 
+
 def get_genre_data(request, user_secret):
-    """Return genre data needed to create the graph user.
+    """Return genre data needed to create the graph
     TODO
     """
     user = User.objects.get(secret=user_secret)