Factor out common parts of room creation

Take the duplicated code out of MatrixChat and MemberInfo, and put it in a
separate 'createRoom' module

src/createRoom.js

@@ -0,0 +1,86 @@
+/*
+Copyright 2015, 2016 OpenMarket Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+var MatrixClientPeg = require('./MatrixClientPeg');
+var Modal = require('./Modal');
+var sdk = require('./index');
+var dis = require("./dispatcher");
+
+var q = require('q');
+
+/**
+ * Create a new room, and switch to it.
+ *
+ * Returns a promise which resolves to the room id, or null if the
+ * action was aborted or failed.
+ *
+ * @param {object=} opts parameters for creating the room
+ * @param {object=} opts.createOpts set of options to pass to createRoom call.
+ */
+function createRoom(opts) {
+    var opts = opts || {};
+
+    var ErrorDialog = sdk.getComponent("dialogs.ErrorDialog");
+    var NeedToRegisterDialog = sdk.getComponent("dialogs.NeedToRegisterDialog");
+    var Loader = sdk.getComponent("elements.Spinner");
+
+    var client = MatrixClientPeg.get();
+    if (client.isGuest()) {
+        Modal.createDialog(NeedToRegisterDialog, {
+            title: "Please Register",
+            description: "Guest users can't create new rooms. Please register to create room and start a chat."
+        });
+        return q(null);
+    }
+
+    // set some defaults for the creation
+    var createOpts = opts.createOpts || {};
+    createOpts.preset = createOpts.preset || 'private_chat';
+    createOpts.visibility = createOpts.visibility || 'private';
+
+    // Allow guests by default since the room is private and they'd
+    // need an invite. This means clicking on a 3pid invite email can
+    // actually drop you right in to a chat.
+    createOpts.initial_state = createOpts.initial_state || [
+        {
+            content: {
+                guest_access: 'can_join'
+            },
+            type: 'm.room.guest_access',
+            state_key: '',
+        }
+    ];
+
+    var modal = Modal.createDialog(Loader);
+
+    return client.createRoom(createOpts).finally(function() {
+        modal.close();
+    }).then(function(res) {
+        dis.dispatch({
+            action: 'view_room',
+            room_id: res.room_id
+        });
+        return res.room_id;
+    }, function(err) {
+        Modal.createDialog(ErrorDialog, {
+            title: "Failure to create room",
+            description: err.toString()
+        });
+        return null;
+    });
+}
+
+module.exports = createRoom;