feat(App): remove obsolete config prop

It's obsolete now, since config is handled in Redux. Also add a "defaultUrl"
prop so emdedding applications can select what the default base URL is.

react/config.js

-/* global config */
-
-// For legacy reasons, use jitsi-meet's global variable config.
-export default typeof config === 'object' ? config : undefined;

react/features/app/components/AbstractApp.js

 
 declare var APP: Object;
 
+/**
+ * Default URL to be loaded if no other was specified using props.
+ */
+const DEFAULT_URL = 'https://meet.jit.si';
+
 /**
  * Base (abstract) class for main App component.
  *
      * @static
      */
     static propTypes = {
-        config: React.PropTypes.object,
+        /**
+         * Default URL to be loaded by the app when not in any room.
+         */
+        defaultUrl: React.PropTypes.string,
+
+        /**
+         * (Optional) Redux store for this app.
+         */
         store: React.PropTypes.object,
 
         /**
     _createElement(component, props) {
         /* eslint-disable no-unused-vars, lines-around-comment */
         const {
-            // Don't propagate the config prop(erty) because the config is
-            // stored inside the Redux state and, thus, is visible to the
-            // children anyway.
-            config,
+            // The defaultUrl property was introduced to be consumed entirely by
+            // AbstractApp.
+            defaultUrl,
             // Don't propagate the dispatch and store props because they usually
             // come from react-redux and programmers don't really expect them to
             // be inherited but rather explicitly connected.
             }
         }
 
-        // By default, open the domain configured in the configuration file
-        // which may be the domain at which the whole server infrastructure is
-        // deployed.
-        const { config } = this.props;
-
-        if (typeof config === 'object') {
-            const { hosts } = config;
-
-            if (typeof hosts === 'object') {
-                const { domain } = hosts;
-
-                if (domain) {
-                    return `https://${domain}`;
-                }
-            }
-        }
-
-        return 'https://meet.jit.si';
+        return this.props.defaultUrl || DEFAULT_URL;
     }
 
     /**

react/features/app/components/App.web.js

      *
      * @static
      */
-    static propTypes = AbstractApp.propTypes
+    static propTypes = AbstractApp.propTypes;
 
     /**
      * Initializes a new App instance.

react/index.native.js

 import React, { Component } from 'react';
 import { AppRegistry, Linking } from 'react-native';
 
-import config from './config';
 import { App } from './features/app';
 
 /**
 
         return (
             <App
-                config = { config }
                 url = { this.state.url } />
         );
     }

react/index.web.js

 
 import { getJitsiMeetTransport } from '../modules/transport';
 
-import config from './config';
 import { App } from './features/app';
 
 const logger = require('jitsi-meet-logger').getLogger(__filename);
     logger.log('(TIME) document ready:\t', now);
 
     // Render the main Component.
-    ReactDOM.render(
-        <App config = { config } />,
-        document.getElementById('react'));
+    ReactDOM.render(<App />, document.getElementById('react'));
 });
 
 /**