do not send band session join notification to band members

ruby/lib/jam_ruby/models/notification.rb

@@ -539,8 +539,13 @@ module JamRuby
           notifications, online_followers, offline_followers = [], [], []
           notification_msg = format_msg(NotificationTypes::BAND_SESSION_JOIN, nil, band)
 
-          band.followers.each do |bf|
-            follower = bf.user
+          followers = band.followers.map { |bf| bf.user }
+          
+          # do not send band session notifications to band members
+          followers = followers - band.users
+
+          followers.each do |f|
+            follower = f
             notification = Notification.new
             notification.band_id = band.id
             notification.description = NotificationTypes::BAND_SESSION_JOIN