Clean up stale data presence on a #newday command

Data presence was not reset on a new day cleanup, while it
is almost certainly stale at this point. Hopefully.

Change-Id: Ifc4cdedf6c365f92e5ff001d1485c8fee21b396f

README.rst

@@ -182,7 +182,8 @@ You have to be a channel operator (+o) to use admin commands.
   Removes active entries for specified track(s)
 
 ~newday
-  Removes now/next/location entries, to be run at the start of a new day
+  Removes existing now/next/location/presence entries. This command is
+  meant to be run at the start of a new day
 
 ~motd LEVEL MESSAGE
   Adds a message of the day on top of the rendered page. Level must be one of

ptgbot/db.py

@@ -191,6 +191,7 @@ class PTGDataBase():
         self.data['now'] = OrderedDict()
         self.data['next'] = OrderedDict()
         self.data['location'] = OrderedDict()
+        self.data['last_check_in'] = OrderedDict()
         self.clean_motd()
 
     def empty(self):