Start to factor out session-loading magic

Take some of the magic out of MatrixChat.componentDidMount() into a new
component.

Also delete the MatrixChat test. It wasn't really doing much, is broken by the
change, and I am replacing it with (better) app-level tests in the vector
project.

src/Lifecycle.js

@@ -26,7 +26,9 @@ import dis from './dispatcher';
  */
 function setLoggedIn(credentials) {
     credentials.guest = Boolean(credentials.guest);
-    console.log("onLoggedIn => %s (guest=%s)", credentials.userId, credentials.guest);
+    console.log("onLoggedIn => %s (guest=%s) hs=%s",
+                credentials.userId, credentials.guest,
+                credentials.homeserverUrl);
     MatrixClientPeg.replaceUsingCreds(credentials);
 
     dis.dispatch({action: 'on_logged_in'});