Implement new replace_state and changed prev_state

`prev_state` is now a list of previous state ids, similiar to
prev_events. `replace_state` now points to what we think was replaced.

synapse/handlers/profile.py

@@ -17,7 +17,6 @@ from twisted.internet import defer
 
 from synapse.api.errors import SynapseError, AuthError, CodeMessageException
 from synapse.api.constants import Membership
-from synapse.api.events.room import RoomMemberEvent
 
 from ._base import BaseHandler
 
@@ -196,10 +195,7 @@ class ProfileHandler(BaseHandler):
         )
 
         for j in joins:
-            snapshot = yield self.store.snapshot_room(
-                j.room_id, j.state_key, RoomMemberEvent.TYPE,
-                j.state_key
-            )
+            snapshot = yield self.store.snapshot_room(j)
 
             content = {
                 "membership": j.content["membership"],