Implement track/stream

* Add Streamer class
* Use FactoryGirl for factories
* Add sha256 field to tracks
* Add mime_type field to tracks

features/step_definitions/playlists_step.rb

@@ -1,3 +1,3 @@
 Given /^a playlist named "([^"]*)"$/ do |name|
-  Playlist.create!(:name => name)
+  Factory.create(:playlist, :name => name)
 end

features/step_definitions/tracks_step.rb

@@ -1,5 +1,7 @@
 Given /^a track named "([^"]*)"$/ do |name|
-  @track = Track.create!(:name => name)
+  @track = Factory.create(:track, :name => name)
+  file = File.new("#{Rails.root}/features/fixtures/test.mp3")
+  @track.save_with_file(file, 'audio/mpeg')
 end
 
 Then /^I should see an audio player$/ do
@@ -8,4 +10,6 @@ end
 
 Then /^it should provide an audio stream for "([^"]*)"$/ do |name|
   page.should have_xpath "//audio[@src='#{stream_track_path(@track)}']"
+  get find('audio')[:src]
+  last_response.status.should == 200
 end