Prepare for asynchronous e2e APIs

the js-sdk is making some of its APIs asynchronous, and adding an `initCrypto`
method which you have to call.

Particular methods we need to worry about are:

* `getStoredDevice`
* `getStoredDevicesForUser`
* `getEventSenderDeviceInfo`
* `isEventSenderVerified`

src/MatrixClientPeg.js

@@ -78,6 +78,18 @@ class MatrixClientPeg {
     }
 
     async start() {
+        // try to initialise e2e on the new client
+        try {
+            // check that we have a version of the js-sdk which includes initCrypto
+            if (this.matrixClient.initCrypto) {
+                await this.matrixClient.initCrypto();
+            }
+        } catch(e) {
+            // this can happen for a number of reasons, the most likely being
+            // that the olm library was missing. It's not fatal.
+            console.warn("Unable to initialise e2e: " + e);
+        }
+
         const opts = utils.deepCopy(this.opts);
         // the react sdk doesn't work without this, so don't allow
         opts.pendingEventOrdering = "detached";