Implement track/stream

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

app/models/track.rb

@@ -1,17 +1,18 @@
 class Track < ActiveRecord::Base
   validates_presence_of :name
+  validates_presence_of :mime_type
+  validates_presence_of :sha256
 
-  after_create :save_file
-
-  def uploaded_file=(file)
-    @file = file
+  def filepath
+   "#{Rails.root}/data/tracks/#{sha256}"
   end
 
-  def save_file
-    if @file
-      File.open("#{Rails.root}/data/tracks/#{id}", 'w') do |f|
-        f.write @file.tempfile.read
-      end
+  def save_with_file(file, mime_type)
+    self.sha256 = Digest::SHA256.file(file.path).hexdigest
+    self.mime_type = mime_type
+    File.open(filepath, 'w') do |f|
+      f.write file.read
     end
+    save!
   end
 end