Calling support

ts/types/Calling.ts

@@ -0,0 +1,8 @@
+// This must be kept in sync with RingRTC.CallState.
+export enum CallState {
+  Prering = 'init',
+  Ringing = 'ringing',
+  Accepted = 'connected',
+  Reconnecting = 'connecting',
+  Ended = 'ended',
+}