Implement actor-model system and start moving Person actor to it

This patch makes Vervis temporarily unusable, because all actors' inbox POST
handlers use the new system, but the actual federation handler code hasn't been
ported. The next patches will port all the S2S activities supported so far, as
well as C2S.

th/models

@@ -23,8 +23,13 @@ Instance
     UniqueInstance host
 
 RemoteObject
-    instance InstanceId
-    ident    LocalURI
+    instance  InstanceId
+    ident     LocalURI
+    -- fetched   UTCTime  Maybe
+
+    -- type      Text     Maybe
+    -- followers LocalURI Maybe
+    -- team      LocalURI Maybe
 
     UniqueRemoteObject instance ident
 

th/routes

@@ -129,6 +129,7 @@
 /ssh-keys                         KeysR      GET POST
 /ssh-keys/#SshKeyKeyHashid/delete KeyDeleteR POST
 
+--/publish/comment     PublishCommentR    GET POST
 /publish/offer-merge PublishOfferMergeR GET POST
 /publish/merge       PublishMergeR      GET POST