VoIP virtual rooms, mk II

Does a thirdparty protocol lookup to the homeserver to get the
corresponding native/virtual user for a matrix ID. Stores the
mappings in room account data. Involves some slightly nasty workarounds
for that fact that room account data has no local echo.

src/dispatcher/actions.ts

@@ -106,4 +106,11 @@ export enum Action {
      * XXX: Is an action the right thing for this?
      */
     PstnSupportUpdated = "pstn_support_updated",
+
+    /**
+     * Similar to PstnSupportUpdated, fired when CallHandler has checked for virtual room support
+     * payload: none
+     * XXX: Ditto
+     */
+    VirtualRoomSupportUpdated = "virtual_room_support_updated",
 }