Test Crypto in Browser

# Testing export/import of Olm devices in the browser

- Make sure you built the current version of the Matrix JS SDK (`yarn build`)
- copy `olm.js` and `olm.wasm` from a recent release of Olm (was tested with version 3.1.4) in directory `lib/`
- start a local Matrix homeserver (on port 8008, or change the port in the code)
- Serve this HTML file (e.g. `python3 -m http.server`) and go to it through your browser
- in the JS console, do:

      aliceMatrixClient = await newMatrixClient("alice-"+randomHex());
      await aliceMatrixClient.exportDevice();
      await aliceMatrixClient.getAccessToken();

- copy the result of `exportDevice` and `getAccessToken` somewhere (not in a JS variable as it will be destroyed when you refresh the page)
- refresh the page (F5) to make sure the client is destroyed
- Do the following, replacing `ALICE_ID` with the user ID of Alice (you can find it in the exported data)

      bobMatrixClient = await newMatrixClient("bob-"+randomHex());
      roomId = await bobMatrixClient.createEncryptedRoom([ALICE_ID]);
      await bobMatrixClient.sendTextMessage('Hi Alice!', roomId);

- Again, refresh the page (F5). You may want to clear your console as well.
- Now do the following, using the exported data and the access token you saved previously:

      aliceMatrixClient = await importMatrixClient(EXPORTED_DATA, ACCESS_TOKEN);

- You should see the message sent by Bob printed in the console.