fix (schedule): Setting tweaks and more bugfixes.

Add the schedule dashboard to the config dashboard.
Move the schedule cost to the second page.
Allow categories to be selected for the session room.

Fix an issue where blacklist role would be checked with no guild data.
Fix typos in session unloading.
Delay session notification.
More logging.

src/modules/schedule/settings.py

@@ -98,13 +98,15 @@ class ScheduleSettings(SettingGroup):
             "During (and slightly before) each scheduled session, all members who have booked the session "
             "will be given permission to join the voice channel (via permission overwrites). "
             "I require the `MANAGE_CHANNEL`, `MANAGE_PERMISSIONS`, `CONNECT`, and `VIEW_CHANNEL` permissions "
-            "in this channel, and my highest role must be higher than all permission overwrites set in the channel."
+            "in this channel, and my highest role must be higher than all permission overwrites set in the channel. "
+            "Furthermore, if this is set to a *category* channel, then the permission overwrites will apply "
+            "to all *synced* channels under the category, as usual."
         )
         _accepts = _p(
             'guildset:session_room|accepts',
             "Name or id of the session room voice channel."
         )
-        channel_types = [discord.VoiceChannel]
+        channel_types = [discord.VoiceChannel, discord.CategoryChannel]
 
         _model = ScheduleData.ScheduleGuild
         _column = ScheduleData.ScheduleGuild.room_channel.name