[refactor] Move Mailbot#logo_url and #conference_color to ConferenceHelper

app/helpers/conference_helper.rb

@@ -1,5 +1,8 @@
 # frozen_string_literal: true
 
+DEFAULT_LOGO = 'snapcon_logo.png'
+DEFAULT_COLOR = '#0B3559'
+
 module ConferenceHelper
   # Return true if only call_for_papers or call_for_tracks or call_for_booths is open
   def one_call_open(*calls)
@@ -28,6 +31,24 @@ module ConferenceHelper
     markdown(ticket.description.split("\n").first&.strip)
   end
 
+  def conference_logo_url(conference)
+    if conference.picture.present?
+      conference.picture.thumb.url
+    elsif conference.organization.picture.present?
+      conference.organization.picture.thumb.url
+    else
+      DEFAULT_LOGO
+    end
+  end
+
+  def conference_color(conference)
+    if conference.color.present?
+      conference.color
+    else
+      DEFAULT_COLOR
+    end
+  end
+
   # adds events to icalendar for proposals in a conference
   def icalendar_proposals(calendar, proposals, conference)
     proposals.each do |proposal|