Implement __hash__ method for custom classes (close #45)

Implement a reasonable __hash__ method() for the classes MCGAlbum and
MCGTrack and use a separate id for referencing albums.

mcg/utils.py

@@ -3,6 +3,7 @@
 
 import gi
 gi.require_version('Gtk', '3.0')
+import hashlib
 import locale
 import os
 import urllib
@@ -75,6 +76,15 @@ class Utils:
         return title
 
 
+    def generate_id(values):
+        if type(values) is not list:
+            values = [values]
+        m = hashlib.md5()
+        for value in values:
+            m.update(value.encode('utf-8'))
+        return m.hexdigest()
+
+
 
 
 class SortOrder: