Implement playlist edit feature

* Display playlists as links in index
* Move playlist form in a partial

features/step_definitions/playlists_step.rb

@@ -2,3 +2,7 @@ Given /^Foo and Bar playlists$/ do
   @foo = Playlist.create!(:name => 'Foo')
   @bar = Playlist.create!(:name => 'Bar')
 end
+
+Given /^a playlist named Electro$/ do
+  Playlist.create!(:name => 'Electro')
+end