Catch call failures due to unknown devices

And show a specific dialog that you can then launch the UDD from
(although currently with a 'Send Anyway' button which makes little
sense for VoIP)

src/cryptodevices.js

@@ -0,0 +1,39 @@
+/*
+Copyright 2017 New Vector Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+export function getUnknownDevicesForRoom(matrixClient, room) {
+    const roomMembers = room.getJoinedMembers().map((m) => {
+        return m.userId;
+    });
+    return matrixClient.downloadKeys(roomMembers, false).then((devices) => {
+        const unknownDevices = {};
+        // This is all devices in this room, so find the unknown ones.
+        Object.keys(devices).forEach((userId) => {
+            Object.keys(devices[userId]).map((deviceId) => {
+                const device = devices[userId][deviceId];
+
+                if (device.isUnverified() && !device.isKnown()) {
+                    if (unknownDevices[userId] === undefined) {
+                        unknownDevices[userId] = {};
+                    }
+                    unknownDevices[userId][deviceId] = device;
+                }
+            });
+        });
+        return unknownDevices;
+    });
+}
+