Add venue_photos model and venue_photos admin controller in order to add more images to Venues and allow to delete it.

Show the additional photos in splash. Added fancybox gem for zoom when click on the additional photo.

fix #777

app/models/venue.rb

@@ -1,6 +1,7 @@
 class Venue < ActiveRecord::Base
   belongs_to :conference
   has_many :rooms, dependent: :destroy
+  has_many :venue_photos, dependent: :destroy
   before_create :generate_guid
 
   validates :name, :street, :city, :country, presence: true

app/models/venue_photo.rb

@@ -0,0 +1,9 @@
+class VenuePhoto < ActiveRecord::Base
+  belongs_to :venue
+
+  has_attached_file :photo,
+                    styles: { thumb: '100x100>', large: '300x300>' }
+  validates_attachment_content_type :photo,
+                                    content_type: [/jpg/, /jpeg/, /png/, /gif/],
+                                    size: { in: 0..500.kilobytes }
+end