CreateRoomDialog is rendered before get default_federate value

In React the order of the execution of mount and render functions
is: `componentWillMount --> render --> componentDidMount`

The `CreateRoomDialog` `render()` function is executed before than
the `componentDidMount()` function so the

  `this.defaultNoFederate = config.default_federate === false;`

; instruction which is executed in the `componentDidMount` function
(in `CreateRoomDialog`) is evaluated always after than the rendering
of the page.

Therefore, the obvious issue is that the values obtained from the
`SdkConfig.get()` function (`config.default_federate`) are obtained
later than their usage on `render()`.

This patch makes this change to fix the described issue:

* componentWillMount instead of componentDidMount

Signed-off-by: Pablo Saavedra <psaavedra@igalia.com>

src/components/views/dialogs/CreateRoomDialog.js

@@ -26,7 +26,7 @@ export default React.createClass({
         onFinished: PropTypes.func.isRequired,
     },
 
-    componentDidMount: function() {
+    componentWillMount: function() {
         const config = SdkConfig.get();
         // Dialog shows inverse of m.federate (noFederate) strict false check to skip undefined check (default = true)
         this.defaultNoFederate = config.default_federate === false;