Add basic playlists management

* Index of playlists
* Create a new playlist
* Basic playlist model with mandatory name

features/step_definitions/playlists_step.rb

@@ -0,0 +1,4 @@
+Given /^Foo and Bar playlists$/ do
+  @foo = Playlist.create!(:name => 'Foo')
+  @bar = Playlist.create!(:name => 'Bar')
+end