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.

test/components/structures/MatrixChat-test.js

@@ -1,34 +0,0 @@
-var React = require('react');
-var TestUtils = require('react-addons-test-utils');
-var expect = require('expect');
-
-var sdk = require('matrix-react-sdk');
-var MatrixChat = sdk.getComponent('structures.MatrixChat');
-var peg = require('../../../src/MatrixClientPeg');
-
-var test_utils = require('../../test-utils');
-var q = require('q');
-
-describe('MatrixChat', function () {
-    var sandbox;
-
-    beforeEach(function() {
-        sandbox = test_utils.stubClient();
-    });
-
-    afterEach(function() {
-        sandbox.restore();
-    });
-    
-    it('gives a login panel by default', function () {
-        peg.get().loginFlows.returns(q({flows:[]}));
-
-        var res = TestUtils.renderIntoDocument(
-                <MatrixChat config={{}}/>
-        );
-
-        // we expect a single <Login> component
-        TestUtils.findRenderedComponentWithType(
-            res, sdk.getComponent('structures.login.Login'));
-    });
-});