Create GroupSummaryStore for storing group summary stuff

- Acts as a layer between GroupView and the group APIs that modify the summary individually. This allows for abstraction of getting the new summary once a successful API hit has been done.
 - The plan is to also control the avatar, topic, body of the summary via the same class

src/stores/GroupSummaryStore.js

@@ -0,0 +1,71 @@
+/*
+Copyright 2017 New Vector 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.
+*/
+
+import EventEmitter from 'events';
+import MatrixClientPeg from '../MatrixClientPeg';
+
+/**
+ * Stores the group summary for a room and provides an API to change it
+ */
+export default class GroupSummaryStore extends EventEmitter {
+    constructor(groupId) {
+        super();
+        this._groupId = groupId;
+        this._summary = {};
+        this._fetchSummary();
+    }
+
+    _fetchSummary() {
+        MatrixClientPeg.get().getGroupSummary(this._groupId).then((resp) => {
+            this._summary = resp;
+            this._notifyListeners();
+        }).catch((err) => {
+            this.emit('error', err);
+        });
+    }
+
+    _notifyListeners() {
+        this.emit('update');
+    }
+
+    getSummary() {
+        return this._summary;
+    }
+
+    addRoomToGroupSummary(roomId, categoryId) {
+        return MatrixClientPeg.get()
+            .addRoomToGroupSummary(this._groupId, roomId, categoryId)
+            .then(this._fetchSummary.bind(this));
+    }
+
+    addUserToGroupSummary(userId, roleId) {
+        return MatrixClientPeg.get()
+            .addUserToGroupSummary(this._groupId, userId, roleId)
+            .then(this._fetchSummary.bind(this));
+    }
+
+    removeRoomFromGroupSummary(roomId) {
+        return MatrixClientPeg.get()
+            .removeRoomFromGroupSummary(this._groupId, roomId)
+            .then(this._fetchSummary.bind(this));
+    }
+
+    removeUserFromGroupSummary(userId) {
+        return MatrixClientPeg.get()
+            .removeUserFromGroupSummary(this._groupId, userId)
+            .then(this._fetchSummary.bind(this));
+    }
+}