Implement more embed code

Supported Media Files:
- Youtube
- Vimeo
- Instagram
- Flickr
- Slidershare
- Speakerdeck

close #26

app/models/event.rb

@@ -1,7 +1,7 @@
 class Event < ActiveRecord::Base
   include ActiveRecord::Transitions
   has_paper_trail
-  attr_accessible :title, :subtitle, :abstract, :description, :event_type_id, :people_attributes, :person, :proposal_additional_speakers, :track_id, :video_id, :video_type, :require_registration, :difficulty_level_id
+  attr_accessible :title, :subtitle, :abstract, :description, :event_type_id, :people_attributes, :person, :proposal_additional_speakers, :track_id, :media_id, :media_type, :require_registration, :difficulty_level_id
 
   acts_as_commentable
 
@@ -25,10 +25,16 @@ class Event < ActiveRecord::Base
   accepts_nested_attributes_for :people
   before_create :generate_guid
 
+  def self.media_types
+    media_types = {:youtube => 'YouTube', :slideshare => 'SlideShare',  :flickr => 'Flickr', :vimeo => 'Vimeo', :speakerdeck => 'Speakerdeck', :instagram => 'Instagram'}
+    return media_types
+  end
+
   validate :abstract_limit
   validate :biography_exists
   validates :title, :presence => true
   validates :abstract, :presence => true
+  validates :media_type, inclusion: {in: self.media_types.values}
 
   scope :confirmed, where(:state => "confirmed")