Split core handlers into its own (broken) class.

poezio/core/handlers.py

@@ -46,6 +46,11 @@ try:
 except ImportError:
     PYGMENTS = False
 
+
+class HandlerCore:
+    def __init__(self, core):
+        self.core = core
+
     def _join_initial_rooms(self, bookmarks):
         """Join all rooms given in the iterator `bookmarks`"""
         for bm in bookmarks: