Include event date in folder structure

This changes the folder structure from:

    {prefix}-{topic}/

to

    {prefix}-{topic}/{event_date}

This makes it easier to sort a folder and quickly find the recording and
all related files for a given day.

zoom-sync.rb

@@ -274,7 +274,7 @@ class ZoomSyncher
       end
 
       ext = file_extension(file_type)
-      folder = subfolder(email, topic, file_type)
+      folder = subfolder(email, topic, event_date, file_type)
       filename = sanitize_filename("#{topic}-#{event_date}-#{uuid}-#{index}") + ".#{ext}"
       video_url = file['download_url'] + "?access_token=#{client.access_token}"
       file_size = file['file_size']
@@ -370,11 +370,11 @@ class ZoomSyncher
     end
   end
 
-  def subfolder(prefix, topic, file_type)
+  def subfolder(prefix, topic, event_date, file_type)
     base_name = "#{prefix}-#{topic}"
-    return [base_name, 'audio'] if file_type.casecmp('m4a').zero?
+    return [base_name, event_date, 'audio'] if file_type.casecmp('m4a').zero?
 
-    [base_name]
+    [base_name, event_date]
   end
 
   def file_extension(file_type)