Have unsigned.age appear on all room events

This is useful for a lot of things, like bridges (appservices), VoIP handling, and clients which generally may wish to do something with the field. Might as well include it on every event, despite the recommendation of https://github.com/matrix-org/matrix-doc/issues/1524

event-schemas/examples/core/room_event.json

@@ -3,5 +3,8 @@
     "event_id": "$143273582443PhrSn:domain.com",
     "room_id": "!jEsUZKDJdhlrceRyVU:domain.com",
     "sender": "@example:domain.com",
-    "origin_server_ts": 1432735824653
+    "origin_server_ts": 1432735824653,
+    "unsigned": {
+      "age": 1234
+    }
 }

event-schemas/examples/m.call.answer

@@ -9,8 +9,5 @@
       "type" : "answer",
       "sdp" : "v=0\r\no=- 6584580628695956864 2 IN IP4 127.0.0.1[...]"
     }
-  },
-  "unsigned": {
-    "age": 1234
   }
 }

event-schemas/examples/m.call.candidates

@@ -11,8 +11,5 @@
         "candidate": "candidate:863018703 1 udp 2122260223 10.9.64.156 43670 typ host generation 0"
       }
     ]
-  },
-  "unsigned": {
-    "age": 1234
   }
 }

event-schemas/examples/m.call.hangup

@@ -4,8 +4,5 @@
   "content": {
     "version" : 0,
     "call_id": "12345"
-  },
-  "unsigned": {
-    "age": 1234
   }
 }

event-schemas/examples/m.call.invite

@@ -9,8 +9,5 @@
       "type" : "offer",
       "sdp" : "v=0\r\no=- 6584580628695956864 2 IN IP4 127.0.0.1[...]"
     }
-  },
-  "unsigned": {
-    "age": 1234
   }
 }