Change Cfp scopes to class methods

When no record matches the requested criteria a scope will return all
the records
In this case, if no record can be found we want the result to be nil

Also, make some readability fixes in specs

app/models/cfp.rb

@@ -3,9 +3,6 @@
 class Cfp < ActiveRecord::Base
   TYPES = %w(events booths tracks).freeze
 
-  scope :for_events, (-> { find_by(cfp_type: 'events') })
-  scope :for_tracks, (-> { find_by(cfp_type: 'tracks') })
-
   has_paper_trail ignore: [:updated_at], meta: { conference_id: :conference_id }
   belongs_to :program
 
@@ -79,6 +76,24 @@ class Cfp < ActiveRecord::Base
     (start_date..end_date).cover?(Date.current)
   end
 
+  ##
+  # Finds the cfp for events if it exists
+  #
+  # ====Returns
+  # * +Cfp+ -> The cfp with type 'events'
+  def self.for_events
+    find_by(cfp_type: 'events')
+  end
+
+  ##
+  # Finds the cfp for tracks if it exists
+  #
+  # ====Returns
+  # * +Cfp+ -> The cfp with type 'tracks'
+  def self.for_tracks
+    find_by(cfp_type: 'tracks')
+  end
+
   private
 
   def before_end_of_conference